do 5.0 trannys fit??

Actually you need either a special pilot bushing to put a 5.0 T5 behind a 2.3L, or you have to turn down the nose on the input shaft so that it will fit the stock pilot bearing. I don't know about the clutch situation there though.

Additionally, the 5.0 T5's .68 overdrive would be tough to live with behind a 2.3L. 2.3 T5's have a .81 overdrive.
 
Stinger performance actually makes an adapter plate that will allow you to mate the larger bellhousing from a V8 to your motor. Then you'll have the benefit of a larger flywheel, (gotta buy theirs) clutch and what ever transmission your back pocket will allow.