When Dodge first came out with the L-bodies (Omni, Horizon, 024, TC3), they had not yet developed the 2.2 Liter Chrysler 4-banger. The early models used 1.7L VW gasoline engines, and either a VW manual or automatic transmission. Some used a 1.6L Peugeot engine, but those were pretty rare, and not very desirable. No VW diesels were ever offered from the factory, but it's a short leap from a 1.7L VW gasser to a 1.5 or 1.6L diesel (same block geometry).
Then in '82 or so, the Chrysler 2.2L engine debuted, and Dodge began phasing out the VW powertrains as the 2.2's came online.
The good news is that the motor mount locations never changed on the chassis, only the bracketry changed from the engines and transmissions. That makes it fairly straightforward to swap drivetrains, if you have all the right brackets.
Steve.