Dropping another 4AC in is by far the easiest, but why would you????
Next would be a RWD 4AGE, Either a genuine RWD or a converted one.
Then it would be a FWD 4AGE which you would need to convert to RWD. Around the same difficulty as the 4AGZE although its not that difficulty
And last the 3SGE which needs heaps of work.
EDIT: Plus you need all the efi fuel stuff when converting from carby to efi.