I have a 997 4 banger and while it is cheaper to get into it, if you want to do an engine swap, you'll need to swap in a stronger transmission as well. Once you factor that in, you are in I6 territory.
If you are going to do an engine swap, go with a smallblock V8. I hear the LS2's that are in the new Vette will be available from gm parts. It'd be interesting to drop one in, but the computer controls could be a pain to work.
Older smallblocks would probably be a wiser way to go.
Green Jeep Member #155
Low Output 4 Cylinder Jeep Member #35
Keep moving forward. But keep an eye on history, for if you don't, you are doomed to repeat it.