I've just rebuilt an early 2.0 TS block (circ 97/98 156), with a later cylinder head (circ 2001 156), using the later head gasket.
The pistons touch the valves when cranked over by hand, which tells me there is a difference either in the deck height of the blocks, or throw of the crankshaft.
I had to use the earlier head gasket to remedy this, which is thicker (2mm versus 0.6mm for the later one), so yes there is a difference somewhere, although they look identicle.
I've yet to measure the crank throw and deck heights for comparisson, the pistons are marked with the same No's.
If you use a complete engine from one era or another, you will be alright, but when mixing spares from various units, be careful.