I quickly realized the extent of the work required to swap out all dash wiring etc.
Seemed like a lot of work for a step backwards in engines.
So, with the help of Wikipedia telling me the exact vehicles and years with the 3.8 Series II, I headed to the local Pick N Pull.
I lucked out and found a 1996 Buick Park Avenue Ultra with a Supercharged engine in apparently decent shape. 8 hours later, we walked out with a wheelbarrow full of engine.
Turned out to be a simple plug and play and ran perfectly without a hitch.
Thanks for the help and the opinions here.
I'll second the suggestion that swapping a series I 3.8 into a vehicle that had a Series II would be a heck of a lot of work, as you need to swap out not only the engine bay wiring harness, but the entire under dash and console wiring. A LOT of work, but do-able.