Hi just got a good running (20 years ago) st 400 out of a 65 riviera so what is the best overhaul kit for it. Any problems /improvements I should look for .Jim
A later model valve body is a good way to improve part throttle downshifts. A TransGo -2 shift improvement kit and a torque converter from a 65-67 V6 or 300.
Wouldn't a '65 Riviera ST400 have the wonderful switch-pitch torque converter? Assuming it, and the related internal switch-pitch parts are in usable condition, you might try to talk Bruce Roe into building you one of his S-P electronic controller boxes. Last info I had for him was bcroe@juno.com but that was years ago. If this were me, I'd put the thing in the vehicle and see if it still worked. If it hasn't been exposed to weather (no water inside) it may not need an overhaul. Fresh fluid, fresh filter, try it and see what happens.
I run a Bruce Roe controller on my switch pitch ST-300 and I highly recommend it. Among other things, it adds a low vacuum trigger that always seems to hit at the right time. Love it.