I was armed with no more than a wiring diagram I lifted from Mitchell and soldering tools. The donor car was a '95 Caprice and I was able to utilize the harness, relays, and PDC. My uncle did the reflash. I prefer the OBDI for simplicity's sake. They don't require simulators for the downstream O2 sensors. You'll be able to delete the AIR and EVAP systems with no issues. I recommend retaining the EGR if you can. It's not too complicated -- just takes time. Here's a "budget install" I did on one of my dad's cars.
This one was a little less "budget" I did on one of his others. The donor car was a '96 Fleetwood. It was actually the first one and used a Street and Performance harness and ECM but, as I mentioned earlier, there were issues with their programming. My uncle sorted it out and flashed another ECM for it. Once the bugs were worked out we added the Paxton and flashed a 3rd ECM. There have been no issues with the harness. The ECMs are all OBDI but the OE Fleetwood can be plugged in and runs fine, it just sets codes for the missing items.
I can't seem to locate the other photos of a Chevelle with a '96 Trans Am engine using the Painless harness. Pretty similar to the S&P but I felt the quality and fit was slightly better.