Dunno how your mate did that, I know one guy who installed 1.8 20vt into he's 1985 [maybe 1984, but that doesn't matters] typ85 A80 GTE quattro, tacho, of course, indicated 4x less revs. Probably he's done with that, since that was long time ago, he planned to use four diodes to get signals from all ignition coils. whatever.
If schematics are still needed, here u go ->
http://www.autolib.diakom.ru/CAR/Aud...NG%20DIAGRAMS/