Although I'm not an authority on VW inline engines, a few clarifications.

1) The Audi engine that VW inherited when it bought Auto Union from Mercedes-Benz did not become the VW engine, although it was revised with an overhead cam and used in the early Porsche 924.

2) NSU was big on the rotary engine and 2-strokes when VW bought the company.

3) I'm fairly certain that the VW inline-4 was developed for the Audi 80/Fox that was released during 1972. Later, the engine was enlarged and also extended to become a 5-cylinder and 6-cylinder. All versions had diesel and turbo diesel variations. As a 5 or 6-cylinder, the intermediate shaft was eliminated, and the distributor became cam driven while the oil pump operated via a chain on the crankshaft.

With respects to the ABA 4-cylinder inline engine that was used from '93-'99: 

The engines were very well built initially, but during 1996, they were "decontented". The forged crankshaft, piston oil sprayers, and double valve springs were eliminated. Get an early one if you intend to put it in your Vanagon.