Square nuts and ceramic tube sockets do date it.  But a bit of krud kutter and it will at least LOOK like new!

Impressive, thanks!  Lots of depth in the Collins and Heathkit departments; did I see even a GR64??
But, no Drake at all?

THere is nothing inherent with either servos or steppers that gives position.  Many motors CAN be supplied with back of shaft mounted encoders for position, giving rotor position.  There are a few that give absolute position.  In most cases, a remote encoder is used since what you need is the position of the geared down output (low velocity) shaft, not the motor anyway.  In the big naval gun mounts, it was done with syncro 3 phase systems, you will also find resolver type systems that monitored the rotary position of shafts. 
There is no technical reason why either a stepper or servo could not make a good antenna rotor drive.  Both need a good controller, one that has preset acceleration, speeds, etc.  A stepper has no brushes, which is some advantage outside.  Lower end servos are DC brushed motors, but many now can be had with polyphase brushless drives. 

Not the exact answer you are looking for, but I'll say this anyway.  I used to use the Molex style, and glad I moved away from them.  I even tried the gold plated contacts;  seemed that the "cheap" brass spring action is just not good enough for my uses.  I used them in diving lights, but the issue is still there for any use.  If you insist on that style connector, go to the AMP mate N lock.  Much better holding retention and female grab strength.  Also, can get these in gold plated.  
However, you exact question is mounting in custom sheet metal.  For much of that, I'd go to the small AMP CPC round.  A hole can be easily drilled or better yet, punched with a greenlee punch.  THen, its 4 #6 screw holes;  much easier than home crafting small rectangular shapes.
And, go with Mouser.  Lots of options;  I go to RS sometimes, but it has to be a true emergency. 

I just made up this circuit, using a Telex aircraft headset.  I get about 75mv ac at the mic plug.  Is this enough to drive a Drake T4x?  The manual only calls for a high Z mic, no mention of voltage level.  My T4x is down right now, and I can't test myself, just yet.
73's

What fails, just with age?   My mental list is in this order:  electrolytic caps, paper/foil caps, then what???  Are disc ceramic caps low risk at 40 years of age?  I read that dipped mica caps are stable with age.

Also,  I was doing surgery on a 4 section "electrolytic" cap and I discovered that the cap uses aluminum foil that appears etched, but not oxide covered.  That is, the cap uses paper as the insulator, not AL oxide like modern caps.  I suppose this is how modern caps are so much smaller.

That leads me to think that either the AC line is getting in the audio, or perhaps the transformer is magnetically coupling into the audio tube.  I see the a twisted gray pair leading off of the AC switch, in back of the volume pot.  Make sure yours is twisted as well.  The switch itself, of course, puts 120vac right along side the low level audio preamp wiring.  You mentioned many or all the Twoers have hum?  Did you try reversing the ac line plug into the receptacle?  That's to get the grounded side of the house 120v on the switch.  Beyond that, if the transformer is not shielded (covered in steel), try putting a steel plate between the ac transformer and the 12ax7. 

I'm not sure that Leader scope has calibrated horiz sweep.  No problem, just compare the horiz distance between peaks of the audio ripple (hum) at the speaker to a known 60Hz source, like the filament 12vac.  If the horizontal distance between peaks is the same for each, then that is 60Hz.  If it is half the distance, then it is 120Hz.  This is critical to know, since that will steer this effort to either a line source (60Hz) or a power supply DC ripple source (120Hz).

Hum that persists with DC on the filaments and "no ripple" on the DC supplies pushes this to a new level.. Is the power transformer shielded in these radios?  Is it located close to the 12AX7?  Are there primary or secondary transformer wires in the area of the 12AX7?  Your testing does indicate that ac is coming in between the driver and audio out stage.  Also, what frequency is the hum in the scope waveforms?  I can't quite read the horiz. sweep rate in the pix.  My comments on the transformer/wiring would relate to 60Hz, not 120Hz.  Does the radio use full wave rectifiers?

Core saturation of the 12vac transformer?   Anyway, try 12vdc.  I'm sure you have a source of that nearby; don't forget to disconnect the xformer, of course. 

Yes, pick up the pipes with #6 to your new plate.  Curious why you have picked up the pipes for the equip ground.  Do you have grounded receptacles at the radio room?  Using the supplied branch grounding conductors is the approved way to ground equipment.  Running ground wires from equipment to pipes is no longer approved for equipment grounding.  And, for piece of mind, locate the service grounding conductor, it should attach to the copper water pipe within 5 ft of the building entrance.  It will also likely attach to a ground rod.

Isolation is a tactic that could work, despite the more typical steps to connect (bond) to existing grounded services.  Note for this to work, the antennas, coax(s)  and connectors should be at minimum 2 feet from any house electrical, guttering, or other major metal that would result in flashover during a strike.  At that already assumes that you had already detached the coax and affixed it electrically to your new ground rod(s).  If that is done, then implement your choice.  One more thing, the 100ft bonding run to your home service is not "long" for DC/low freq lightning pulses.  Especially if it is buried in the ground on the way to the service below your roof dripline.  Also, if your home is plumbed with copper cold water, that is a viable method of bonding, since code requires that it be bonded already to you home service.  A water pipe should be a lot closer than 100' away.  If PVC, forget that...

I'm on a 75 x 100 lot and have the same issue.   Even a bit worse, since I work 75m.   Anyway, if you are good with a direct neighbor you might ask if you can run the "other end" of a wire to his/her residence.  In my case, my neighbor 100' away had a tv antenna tower, and surprise-surprise, he lets me tie to it at the 25 foot mark.  Anyway,  just a "out of the box" idea for you.

73's

That is fine for equipment grounding/bonding, but at 14AWG don't put it in the path of lightning!  To deal with possible lightning coming down the coax(s), you NEED to get a larger conductor to bond to a local ground rod (or two) (#6 AWG is fine), and then a larger conductor to bond to your home entrance ground system.  I use a 2" solid strap .020 thick buried on the way.  Georgia Copper has this.  So, it could go like this:   Heavy strap from your coax connector plate to your home service ground system;  #6 AWG solid to run to your local ground rods to the coax plate, and then a braided strap, #12 or larger equiv to your gear inside (from the coax plate).  Also, pick up any surge protectors, UPS, outlet strips to this same braided strap.  This is not an exhaustive treatment, but a decent start.  If there are rotator cables, TV antennas, those need penetration protection as well.  Don't solder any of this.  Use either yellow/red metal connection hardware and/or hard braze. 

I was more worried about the hookup wire.  Now a melted pile of Drake hookup wire in the chassis would be catastrophic.  I think this low end / old pvc is rated at 60 C??  I'm letting the T4 sit for a few weeks, the finals are bad and they are the next step.