interchange

I'm not a slant expert, but a couple of possibilities come to mind if using a later model replacement motor (if I'm mistaken, I'm sure someone will correct me)-
The oil pan/pickup from your original motor will need to be re-used on the new motor.
As stated, a '68 and newer engine needs to have the convertor hub register issue addressed.
Carburetor and throttle linkage from original engine need to be used.
Use all mounting brackets/hardware from the early motor; as a matter of fact, don't get rid of/turn in for core charge the original motor until the new one is in and running. There are all kinds of miscellaneous odds and ends you will need to make the swap go smoothly.
You may need to use the old valve cover; newer models used a PCV valve which may not be compatible with the old carb, older ones used a draft tube.
The man with all the answers is @slantsixdan , but he doesn't shine around as much as he used to... :)