To circle back around from all the thread jacking to the OP's original question: How hard would it be to transplant a 454?
I think if you can find the same type of oil pan sump as your 429, it should fit. I don't know about the oil pump interference, I don't have a 454. There is generally a lot of room in the engine bay on these cars. Could be some steering shaft interference if the 454 is wider than the 429, I doubt it is.
A 454 is not going to mate up with your caddy Turbo 400 though due to the nailhead pattern that is on the stock adapter. You would have to transplant a later model chevy turbo 400 in. It should be easy if you can match up to the same length as the turbo 400 that is in there now. Exhaust, IDK. If you can find factory 454 manifolds that dumps out in the same general location as your stock 429 manifolds I would say it could work with custom exhaust pipes. If not, go with custom headers or block huggers. Your '64 will have only 7 volts to the coil, so swap out that pink wire with a new one at the firewall. The pink wire has internal resistance.
The 454 will still be lighter than the 429 that is in there now, so coils should be fine. I bet the stock radiator is big enough but the inlet and outlet may be on the wrong sides.
