internals are the same.. basically the bellhousing bolt pattern is different (thanks mopar!) how easy? depends on the person.. after you do one you will be able to do it in a hour.. just details and paying attention. there are a couple of books about how to build a 727 that are worth buying..
Also.. go on facebook marketplace you get can 727s from $100-300 all day without dealing with ebay...
BTW! That being said. put that damn 383 in the car! a big block a-body..... come on..