Engine Swaps for a Series I 3800 stock to a Series II Supercharged?

I have a similar issue. I just purchased a 1991 Buick Riviera. It is in cherry condition, single owner, white gloved. It has less than 50k miles on it! No ****!
I have been looking everywhere for supercharger kits, engine swaps, you name it. Haven't found anything that would work to date with minimal retrofitting. Please, if anyone has any suggestions on how I should proceed or where to look I would be very grateful. I have been eyeballing the Series II 3800's, but I just dont know enough to take any action. In the end it would be the mechanics who did the mods, but they are equally short on leads as I am for some reason. Hope to hear from you soon.

God, just look at the Series II L67. Isnt she beautiful?