The Larson NMO2/70 is THE BEST 2/440 mobile antenna made.  The fact that so many public safety agencies use Larson mobile antennas is a testament to their performance and durability.  I use Larson exclusively on all of my mobile installations.

The 1 KFA and 2KFA are outstanding amps.  I've used them extensively though I don't have the spare $$$ to own one myself.  They are well protected, have built in tuner that will handle 3:1 and yes you can use them SO2R.  Expensive but probably the best amps I have ever used.  If I had the budget for it I would get the 1KFA.  Much less money and I doubt the difference of 250 watts would be noticed.  Has all the same features as its big brother.  Will run just fine on a 20Amp 110VAC circuit too.

There have been a lot of hams that have converted 2500's to use available tubes since the originals are pretty much unobtainium

I easily worked DXCC on 40 from the west coast using a 40 meter 1/4 wave vertical.  You should do fine from your QTH

Given that it is LMR400 even at VHF the loss at 90 ft will be negligible.  If you use a properly sealed barrel connector and well installed PL259's and weather seal it well it should be no problem.  I have a run of well over 200 feet (with a barrel at midpoint) between my shack and the base of my tower.  No problem being heard!

I have owned full legal limit amps over the years including Alpha's and the Ten Tec Titan 425.  I currently have an AL 811H which I have had zero problems with.  I run it at 600 watts max and can work anything I want to with it. As you note, with RF Parts warranty on tubes the occasional sour 811 or 572 can be replaced.  If you want a solid amp with a little more output the Al 80B @ 1KW is an economical choice.  Frankly I can no longer justify the big $$$ difference between 700-800 watts and 1500 watts when the benfit in terms of what I can work with the bigger one over the smaller one is so slight.

Alan's site is excellent and I do recommend it.  However, since the OP's question was very specific let me say that I have had great success with the Little Tarheel II.  Use the cowl mount suggested by another poster to get it over some metal.  Bond as much of the metal to the frame as you can using copper strap.  Include bonding the muffler/tailpipe.  You should be good to go and I think you will be happy with the Tarheel II....I know I have been

There are only designated government entities that are permitted on the SHARES Network under a blanket license and individual counties are generally not considered critical enough users for that purpose.  As for the VHF AM Aircraft radio "ground stations" especially portable/mobile ones are generally not considered for licensing.  Conrol towers, FBO's (usually on limited UNICOM frequencies)are and the PCSO comm truck is neither.  From SAR experience in both CA and OR I have never seen the need to use airband for ground, aircraft communications.  Almost every law enforcement, fire, and medical fixed wing or helo I have worked with generally has a multi-band programable radio and can talk to your MCU on the PCSO frequency, CLEMARS, CALCORD, SAR, or some other channel for which PCSO is licensed.  In the case of CAP aircraft, CAP can talk to them from your MCU using their equipment/channels.  I have yet to see a CAP deployment where they did not use one of their own comm people for communications.  In the rare event a private (not CAP) aircraft is used generally the spotter (non pilot crew) is a member of some government entitiy involved in the search.  That person, using a handheld, can communicate to the PCSO MCU on one of the aforementioned channels.

It would be interesting to know whether PCSO is even licensed to use the aircraft and HF radios.  My experience in SAR and in building Mobile Communications Units is that getting licensed to use those radios is not an easy task.

The best approach I've found is to put a pulley and halyard on each support, attach the
halyard to an insulator around the wire (the "egg" types sold for electric fences don't need
to be threaded onto the wire) then hoist it into place.  A counterweight on the bottom of
the halyard limits the stress on the loop when the wind blows - this is particularly important
when using trees as supports.

The above is BYU's advice and that is exactly what I did with my 80 meter horizontal loop...which had 2 of my 4 vertical support posts snap in a 102 MPH wind gust on 12/17/12.  When I re-build it this spring I will be guying the support poles

In the research I did before homebrewing my OCFD (180ft/90 ft on the legs) I read somewhere that the value of the CURRENT balun will vary with the height of the feedpoint.  What I read indicated that if the feedpoint is over 65 ft in height a 6:1 current balun should be used, so that is what I did as mine is fed @ 90 ft with the ends being up about 30 feet.  From the balun my coax run to the remote antenna switch is about 100 ft and the output of the remote coax switch goes to a Polyphazer before the 200 ft run of hardline back to the entry panel at the shack.  My SWR's on the bands the antenna is designed to work on are just fine.

I don't think your folding roof rack will provide a good ground plane.  Others have mounted them on the spare tire mounting frame.  Still others have used a mount off the front fender.  If you haven't checked out K0BG's mobile page (http://www.k0bg.com/) I suggest you do so.  The Atas 120 is not a real efficient antenna so it needs the best ground it can get.  It also has some weatherproofing issues you might want to deal with before you mount it.  Google Atas 120 and you'll find discussions of that

Having owned a LOT of amps over the years I agree with those who suggest the AL 80 (A or B).  Run it on a dedicated 120VAC circuit and you will be fine.  I currently use an AL 811H with 811 tubes, run on a dedicated 120VAC circuit and never run at more than 550 watts.  Works great.  No real advantage to 572B's over 811's.  In fact the quality of 811's is better than the 572B's currently available.  No need for an amp interface either.

If you need to re-tube an 811 amp I suggest RF Parts.  If a tube goes soft during the warranty period they are great on providing a replacement under warranty. Finally, the 10/12 meter mod is simple.  Info on which wire to cut (already suggested by another) as well as photos depicting exactly which wire are available on line.

Do NOT mount the Yaesu in a cubby hole like that--the control head yes but NOT the whole radio.  That radio needs ventilation around it.  You mount it in a small space like that with no air circulation around it and it will not last long.  Heat build up is its worst enemy

Curious why you used a conductive material for your guys.  I use paracord for guys on a 38 ft vertical and we get a lot of wind...no singing