look for a 2.0 16v k-jet lump block out of a passat or corrado, and it'll be a 9a. Find a 2.0 16v k-jet lump out of an audi and it'll be a 6a, which is same as 9a but with audi bits bolted on (sump, oil filter housing etc)
2.0 16v digifant out of a MK3 golf or seat will be an abf, which is a bit taller than a 9a or 6a (and a KR).
The engine codse is stamped on a flat area at the top of the block between cyls 3 & 4, but almost without fail this will have corroded away, so you'll need to use the sticker in the boot of the car or the inside cover of the service book.