Mainly due to the fuel rail mate .

Be a good little project that bud.....I used 1mm machined pistons (7.8:1) in my old ZVH. I'd rather have machind pistons anyday over a spacer plate, at least you have propper sealing between head and block then!.

If you need any help mate, jus shout PS. is it a 1.8 or 2ltr?