Hello again
After fitting the valve springs the valves would not open, there may be different ones for inlet and exhaust which I got muddled, was advised to put the standard ones back in and worry about it later if it became a problem.

I also paid near £150 for the head gasket and with £200 for an st170 engine I now believe it would have been better to have done something to the pistons, RS ones do come up for sale or even Vauxhall ones or spend that little bit more and get aftermarket ones.

It is my understanding that a standard engine will work fine at low boost with decent mapping so instead of buying decomp plates or thicker gaskets and an oem ecu the money might be better spent on an aftermarket ecu like a megasquirt

just a thought