Hi,
I would say that is always a hard decision to make. NA 2.3L, turbo2.3L or 5.0.
Easiest and cheapest would be keeping what you have and doing a few of the modifications found in this forum: Cold Air Induction, Roller cam from a ranger, Ranger header, maybe gut the cat or replace the exhaust. Many of these things can be done cheap if you manage to find them at a wrecking yard. The downside is your only going to get a little more power than the weak stock engine. Still it's more that it had before. Oh maybe stock is about 88-90hp. With these mods you may be at 100-110, maybe a tad more.

But it's cheap and easy to do and you shouldn't have to worry about to many issues you wouldn't have had from a stock setup.
TURB 2.3l swap= Different and Lots more power. Lot's more work too! Do lots of reasearch first. Tuning can be an issue and degugging problems seem to be common. But if you have the skills and money it might be a fun thing to do.
5.0 swap=POWER and sound and $. You will have the easiest time getting power here. Tons of parts are available. But you need an engine and any wiring, transmission, motor mounts, you should also get an 8.8" rear end. Possibly you'll want v8 brakes. fuel lines should be moved so as to not be too close to the exhaust. The best way is to find a wrecked 87-93 mustang and swap the parts over. There is a lot of info on how to do it.
So I'd think about this.... Could I REALY do this? Do I have somebody that can and will help? Am I motivated to finish this? Hear's a big one: Do I have $ to do this. Trust me, you'll probably spend more than you expect in a swap. especialy if something ends up needing repaced or rebuilt.
So, if you don't have a ton of money or knowlege I would do lots of research on the web and save my money. Then decide. It's cool to have a fast car, but it's still fun to work with what you've got and make trips to the salvage yards and pick up parts cheap and get that car a little faster and still not have to worry about money or gas milage or reliability etc.
BTW. You could still find used wheels. a deal on lowering springs. 5.0l sway bars at the yard etc to make it look as good a 5.0l and handle better around the corners.
So many things to think about. Whatever you do, make sure you have fun.
