ol Skull,
Been my findings that the M-18's run in the #90 range.
I have 4 engines that reflect that.
One engine has new .010 overbore, pistons & rings and about 50 hrs running time and both cyl read #92
The M-20 is stroked a bit, so it could run higher, they say + or - 10%
and with carb butterfly wide open
You can check valve clearance, but I say run it a bit and get a "feel" for it.
