You would have to calculate the combustion chamber volume required.
composite gasket heads have 28Cc combustion chambers and shim gasket heads 35CC?
40 thou shave takes a shim head to composite head.
So I reckon about 20 thou.
You will have 3 potential problems
1 You will need pedestal shims to get your lifter preload to between 20 thou and 60 thou.
2 The heads will be soft if you believe the LR stuff.
3 The inlet manifold may need machining.
The correct way is different pistons.
Regards PhilipA
PS 8.7 :1 is just about the limit for even 95octane as the head design is old.
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