1975 cutlass supreme engine swap

I believe these cars were still coming equipped with actual Buick engines, so any Buick engine from that era will be a relatively easy swap. Not too long after that they started putting Chev small blocks in all their cars. Going back to your car any small block Chevy engine will also be a relatively easy swap as there is ample room in the engine bay and a lot of similarities to the engine the car came with. However, do your homework. Some things don't fit and will have to be fabricated or purchased and some of those parts are not cheap. I'm not sure about your transmission, but I believe it will bolt up to a small block Chevy, but I'm not certain, so once again, do your homework before you dive into something you can't or don't want to finish.

I think muron is right about the Buick engine however a SBC swap would not be hard as you can use parts for other A body GM cars of that era (Chevy, Olds, Pontiac).