As already stated, I used the stock TH325-4L tranny, which is good for a daily driver, but if anyone wanted to put a Chevy, Olds, or Buick motor with performance mods- or drive a stock Caddy motor they way it begs to be driven, the TH325s won't hold up. Here are some pictures of custom mounts that can be made to swap in the stronger TH425 . Adaptor plates also need to be made to mate the bigger tranny dif to the smaller CV axles. Some hammer mods required for lower part of firewall.
BYW: as pictured, I have less than $2,500 invested in the whole car project (including the cost of the car) and used totally stock salvage yard parts.