90 Cadillac STS Engine Swap
 

I have a 90 STS with a 4.5,273/multi port fuel injection V* . Considering a swap to get an Allante 1991 4.5 liter installed. Is it possible??? Do I need to change ECM or other hardware? would it be worthwhile from a performance perspective?

it will physically fit, the "Tune Port" style manifold should give better performance. It's definitely worth trying. You may need to adjust some wiring but not much of it. You may need to tune it afterwards, but I think it should work I with the STS electrical. I would try it and also get all the spare Allante' stuff I could in case it needs tweaked