Ok, so i have a 1987 Buick LeSabre with the 3.8L HO and its FWD.

I was wondering if anyone knows cross compatability between subframes
to conver to a RWD car that im dropping a 5.7L in. I was thinkin
a regal subframe or whatnot...thanks if u can help.

without significant modification, i dont think that any swap will be easy

Well, i changed my mind, and im getting a engine/trans/ECM out of a supercharged gtp.