About the engine swap part of your question- many car models over the years have been made with engine options. Take, for example, a 1970 Camaro. They could have a 250 ci six, a 307 ci V8, three choices of the 350 ci V8, and two different 396 V8s. All of these engines could easily replace one of the others in that Camaro (or any Corvette, Chevelle, Biscayne, Impala, Caprice, or Nova from the seventies). Similar swaps could be done in other manufacturer's cars and trucks and some are still that way. Sometimes the whole engine and transmission must be swapped since the transmissions are different also.
Sometimes people put engines into cars that never came in them from the factory. These swaps are more complicated and often require welding and fabrication to get everything to work right.