Welcome to the board.

The short answer to your question is that only the Isuzu 3.2 and 3.5 engines will be a simple swap. Anything else is going to require effort and fabrication.

To get a better understanding of what you're looking for though, what do you mean when you say "worthwhile"? These engines are generally pretty stout and functional. What are you looking for out of your powerplant?

James