Does a Chevy 305 motor fit 80 Buick regal?

A Chevy 305 small-block engine will *not* fit directly into a 1980 Buick Regal without significant modifications. The Buick Regal of that year used a different engine mounting configuration and transmission bellhousing pattern than the Chevrolet small block. You'd need custom motor mounts, a custom transmission adapter, and likely modifications to the firewall and possibly other components to make it work. It's a major undertaking, not a simple bolt-in swap.