Are you 100% sure about the combustion chamber on the different heads? I´ve been looking for ages for info on this, no luck until now.

A 1.8 egnine has a CP ratio of 10.0:1

Wich means that with combustion a chamber of 45cc a compressed cylinder head gasket of 0.96mm thick would be needed to reach 10.0:1

45cc = 0,96mm for 10.0:1

44cc = 1,15 mm for 10.0:1

43cc = 1,35 mm for 10.0:1

Above figure on a standard engine with a 88mm stroke and 80.6mm bore

So using a 2.0 head with 1.8 block would give you the following:

47cc combustion of 2.0 head

0,96 mm = 10.48:1

1,15 mm = 10.29:1

1,35 mm = 10.10:1

46cc combustion of 2.0 head

0,96 mm = 10.67:1

1,15 mm = 10.47:1

1,35 mm = 10.27:1

45 cc combustion of 2.0 head

0,96mm = 10.86:1

1,15 mm = 10.65:1

1,35 mm = 10.44:1

Above figure on a standard engine with 88mm stroke and 84.8 mm bore