Ive got both a mk2 with the abf 2.0 16v engine from a mk 3 and a mk2 16v with a passat 2.0 bottom end. To be honest i like the origional 16v with the 2.0 conversion better because it seems more responsive bottom end. I think the abf is probably slightly quicker and has more pull top end but for the time effort and cost it would take to do a swap i wouldent bother.
P.S Im selling the car with the ABF conversion. Looking for about ?2000 its in imaculace condition.