I have pictures, but no web space to link them to here.
Wiring! Lotsa wires, everywhere. I used the painless harness. I would not go that route again. There are at least two companies that offer to take your existing harness and remake it to run the new engine. They are expensive though.
Be sure to get a complete engine. I had a partial and it took forever to track down the parts I was missing.
Exhaust was a pain. The 91 was never intended to have dual exhaust. I needed a new hangers welded in, and needed to convert to a 94-96 transmission crossmember.
If you plan on keeping AC, you're going to need all of the 94-96 lines. You will also need to dent the motor mount crossmember to clear the compressor.
The passenger side motor mount needs to be moved about a half motor mount to the rear.
Fuel lines and fuel pump need replaced.
Transmission cooler lines are different.
Power steering lines are different.
The condensor is much thicker on my car, so we had to fabricate different rubber mounts for it.
I used stock Impala fans. But any aftermarket electric fan should be fine.
You CAN use your stock radiator! I didn't use mine because I needed the mounting points for the Impala fans.
If I remember anything else, I'll post later.