If the 8V has valve relifes in the pistons you should be ok. If they don't you'll have to swap the motor because the 16V engine is a interference type.
The 8v pistons have reliefs for just the two big valves. I doubt they would work with a 4 valve head, plus aren't there differences in the alignment of the cam belt and oil/coolant ports?
The 8V pistons don't really have reliefs as it's not a interference engine but your right the 8V pistons wont work. There are no differences in cam belt or oil/coolant ports. Just don't installed the wrong head gasket or install it upside down as it will block a oil passage.
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