Im doing an engine mod....can a gm crate 502 fit in a 1985 buick regal. i have seen a 84 cutlass with a 454 ?

The Cutlass and Regal are basically the same engine bay, frame, etc... If a 454 fit into one, then a 502 will, but beware, there may have to be some cutting done. I've installed an Olds 455 which is a massive engine, into an 84 Cutlass, I had to cut a hole in the A/C housing to allow room for the valve cover. It was a small hole about the size of a half dollar coin. just be prepared to make some modifications, other than that shouldn't be a problem.