Saab b234 in a stang!?

I doubt you'll find much on swapping a foreign I4 into these cars; given that the V6 uses a small block mount, the common upgrade path is to go small block, or to swap K members and go modular. But, as my dad always said, you can put any motor in anything as long as your wallet supports it.

The V6 should be a T5 transmission. Depending on your power output, that may suffice.

The other things that come to mind are the gauges and fuel pump, both computer controlled in a 2001. You can swap in an older set of gauges (common in Coyote swaps too), which would just need to be fed the correct inputs for each gauge, or go full custom. Fuel pump I can't say (I've not looked at it that much myself), but I know people have swapped to a return style system (using a constant pressure pump), so you may want to look there.

F*** it. I'm prius swapping my mustang.