xlowerx
+1y
Depends on what you consider difficult. Your going to have to remove your existing motor, radiator, transmission. Then you will need to weld in new motor mounts for the 350, get a larger radiator. If your going like LS route, you'd need to get a complete wiring harness to run the computer OR if you go carberated, then you could get away with a much smaller harness.
Then you'd have to figure out which tranny you want, manual or auto...
I'd say its not an easy swap. But if you have time, patients, and money, I'm sure you could pull it off.