I had a Model B cylinder head cut to raise the compression ratio by eliminating the reliefs in the head for the pistons plus some more material.
Using clay on the piston tops, I determined the overall clearance (including piston protrusion above the block deck and the gasket thickness) was 0.010".
I ran the motor at a car speeds of 65 to 75 mph with stock differential gears, and initially the pistons did not come into contact with the cylinder head. However, once carbon built-up on the piston tops, there came a horrible knocking sound as the clearance between the head and pistons went to zero. That ended my experiment with a shaved cylinder head.
The right way is to run a cylinder head with combustion chamber shapes designed for high compression. Reliefs in the head for piston clearance are a necessity.