I vaguely remember (a LOT of years ago, maybe mid to late 70's??) an article in "hot rod" magazine that talked about a kit that was available at the time to put a volks engine in a Vega. The early engine was a real problem in these cars, they were pushing the volks engine as a solution. REALLY wish I still had the mag..........
The kit would look after hooking the volks engine to a GM driveline. All but the earliest Vega/Astres had the standard GM trans mount, usually a saginaw 4 speed, occasionally the aluminum 5 speed. Had one I put a 3.8 Buick in a lot of years ago............ had the bad engine, only the last ones came with the "iron duke" 2.5l engine.
love to hook a 1.9 or mtdi to a GM rwd trans, think small blazer, S10, maybe the 82 firebird I've got sitting in the back yard. Currently has a 400 smallblock with the same saginaw trans that came in the vega.......