I'm in the midst of resurrecting a late 500C myself; all electrolytic caps have been replaced as was R-203 (4.7K 1 Watt) which I replaced with a 3 watt non-inductive thick-film resistor (the original had badly overheated, and was only 3.3K).
Be aware that the 500C went through some changes during its production run; I've read that there are as many as 7 variants. Biggest is early vs. late; early has only a 3-position function switch, late has a 5-position switch.
Early version has an additional transistorized buffer stage in the VFO as an attempt at stability which was dropped in the later version; late has a solid-state carrier oscillator which replaced a tube stage (V14 & associated components).
As a result, you'll need to ID which version you have and use an appropriate schematic, but expect that it won't be 100% accurate. The parts list in the manual may not be 100% accurate either - the manual I found for my late 500C shows C202 as a three-section electrolytic cap (40-40-20 uf @ 450-450-25 V), while the Mallory original one installed in mine was only a two-section (40-40 uf @ 450-450 V); the schematic in that manual shows a C202a (40 uf @ 450 V)and a C202c (also 40 uf @ 450 V) but I can find no C202b in it...
I went the complete power supply board replacement route; bought the kit & assembled it. Depending upon the mounting tolerances in your PS, you may need to use spacers to mount the board in order to clear the transformer - mine took about 1/4" to clear.
Also, one of the tubes (I think the 6GK6 driver - I'm working from memory here) has pin 6 tied to ground; with original tubes this poses no problem but some replacement tubes have internal connections which will cause the "magic smoke" to escape if pin 6 is at ground potential. The fix is to remove the ground connection for pin 6 at the tube socket (i.e., nothing connected at all to pin 6). (Verify which tube first, before doing anything - as I said, I'm working from memory here...)
I've been considering the K4DBK VFO stablizer ( http://www.eham.net/reviews/detail/7448
), but want to get the 500C working as originally built before considering any add-ons. I've seen a somewhat major mod to replace the PA sweep tubes with 6146 transmitter tubes, but it is rather involved; I doubt it's something for a neophyte to tackle, as it involves new tube sockets & rewiring of the PA stages.
Finally, check out the Swan group on Yahoo - good, helpful people, and a great deal of useful information.