What parts on a 1971 Chevelle are interchangable?

Interchangeable with what? Nearly all of the body and interior parts interchange with a 1971 Chevelle. Most of the body and interior interchanges with a 1970 Chevelle as well. Rear axle interchanges with ANY '68-'72 GM A body. Engine and transmission interchanges with any Chevy from the 1950's up to the 1990s at least. Front suspension also interchanges with ALL GM A bodies. All small block radiators are interchangeable. All big block radiators are interchangeable. It all really depends on what part you are trying to use/replace.