I just purchased two old school Jettas for very cheap.
I'm new to VWs and know nothing. I need a head for my '90 and was wondering if the 16 valve head would fit on my block and what complications I might run into.
Thanks

You should have little to no problems - A1's and A2's are Golf and Jetta body codes - which gives you basically a wide array of engine options - including 16 valve, G60, VR6 and 1.8T engine types - these cars were designed to be fabricated - if you had a Fox on the other hand - which has a longitudinal engine - than you could run into probs - but this is a very possible engine transplant project - I say go for it if you can :)

A 16 valve head will fit right onto an 8 valve block, but the pistons are different. They are the same bore & stroke, but the 16 valve pistons have cut outs for the intake valves. Of course you would have to use both manifolds, etc... from the 16 valve also.