It is technically possible, with enough money, time, effort, and parts, to swap in and out of an A4-chassis car, any engine that originally came in any other A4-chassis car. All the parts required - and there could be a lot of them - will bolt directly in. But swapping out a P-D engine to install a distributor-pump engine - although possible - is like moving backwards. Why spend big money to go backwards to older technology?
Strictly speaking, this might not be legal. Due to emission certification I don't think you're supposed to put in an engine that's older than the model year of the chassis unless they have the same emission certification - which they don't, in this case. Possibly nobody would ever figure it out, but that's another story.