I'm very slowly moving towards an Audi 4.2L V8 swap into a 2000 S. Nothing notable for progress yet, but a few comments that I can contribute.
The 32 Valve (ABZ) engine:
Cable throttle.
Bolts right up to the 5-speed transmission.
Did not come with a manual transmission option in the USA.
Has a 10 bolt output on the crankshaft and will need a custom adapter to mate up with any flywheel. 034 motorsports makes one. Looks like they are almost out of stock.
A simpler (probably more reliable) design than the 40V engines, but a little less power.
Very affordable.
40 Valve (AKB, AQF, ART, AUX, AWN....)
Comes in a variety of vehicles: A6, A8, VW Touareg.
eGas throttle.
Bolts right up to the 5-speed transmission.
8 bolt output, can directly use an available flywheel and clutch.
Variable valve timing and a little more power than the ABZ.
Costs more than the ABZ, but still very affordable.
More complex for custom ECU.
***Neither of these is an easy fit and will require some creativity to sort out the height and position of the intake.