16V for '94 2.0L

Would it be possible to replace a 8V to a 16V on a 2.0L?
Would it be possible to put a 20V from a 1.8T on a 2.0L?

Are you asking about swapping those heads onto those engines? If so, then no. 8V & 16V heads are similar, but there are differences in the blocks that make transfering heads too dificult to be worthwhile (16V pistons have valve cutouts, blocks have extra doweling & different oiling). 20V 1.8 engines are radically different than 2.0 engines.