1st Posting/engine swap?

Okay, this is my first posting so be gentle. I was recently given a 91 STE with a blown 3.4L. Without offending the purist, how much of a hassle is it to put a 3.1L in?. Would I be able to use the same ecu, exhaust, trans?. I read that 94% of the STE's came with 3.1's so I wouldn't think it would be too much of a problem. Seems the 3.1 would be easier to find, easier to maintain and less problematic then a 3.4. Thanks in advance.
Bystander

The ECM and wiring harness are different between a 3.4 and a 3.1. You'll need a donor car that you can scavenge those parts from. There may be other issues as well, like motor mounts, exhaust, hoses, etc... that may give you headaches.