The 16 valve motor shares the same bore and bore spacing and uses the same head gasket as the 8 valve version.

The block casting is different as the 16 v version has belt driven oil pump and the cast bosses where balance shaft housings attach to block. The head can't be swapped (if you have enough money for a ton of custom pieces and a special timing belt. so technically it can be swapped, I suppose) as the belt drive and idlers for timing and balance shaft belts aren't designed for the use of 8 valve head on 16V block and vice versa.

There is a 16 valve head used on Volvo boat engines that works on the 8 valve block. This head is used on a 2.5 litre stroked motor so while you're at it get the crankshaft and rods.

The pistons have different tops on the 16v vs. 8v motors also.