Cosworth head gasket question.

Just got my head back from the machine shop and I'm looking at fitting a cosworth gasket. Now, my block is bored 87mm with hks pistons fitted, but I see cosworth only do 87mm and 90mm gaskets. Will the 87mm gasket fit as reading a few posts people are saying you need to be 0.5mm bigger ideally. So basically what I need to know is are the cosworth gaskets 87.5mm stock or can I fit an 87mm gasket or do I need a different one. Sorry if this sounds confusing but I'm in the pub and I'm a bit pissed!

Yes, you should use 87mm gasket. If you go 87.5 then 0.5mm gap is a good spot for detonation. The squashing of the gasket is factored in. I bet you if you measure the bore then it will be 86....something and not dead on 87mm. So relax and have a few more pints.

Woo hoo happy days, I'll put one on order after my next pint!