[AZ64GP]

I'm restoring my '64 GP which is a very original car and I'm trying to keep it as close to stock appearance as I can, except for safety/reliability upgrades like front disc brakes/dual chamber master cylinder, replacing the wiring, etc. It's unique in that it's a factory A/C car with power windows and other options, but it's no 421 tri-power, 4-speed which will be worth high 5 figures either.

Anyway, since it is a "numbers matching car," I've been debating trying to keep the stock Roto 10 (Slim Jim) transmission and having it rebuilt. I know the Slim Jim in it will need to be completely rebuilt (the car sat for 20 years in a dirt lot and transmission wouldn't shift when I bought it), but I'm debating between doing that or swapping in a rebuilt Pontiac TH-400 from the late 60s.

I have read on this forum of all the trouble and expense of rebuilding the Slim Jim and how much better the car will run with the TH-400. For the sake of keeping the car original and what the car may be worth when it's restored, is it worth trying to get the Slim Jim rebuilt? From the folks on this forum who have driven the Slim Jim cars and ones with later model transmissions who did the swap, what would you do? Would swapping a TH-400 make the car less or more desirable than keeping the transmission "numbers matching" with the Slim Jim? I appreciate others experiences, knowledge and opinions. Thank you.