So long as the head still seals properly against the liner there's no problem taking out a shim. Most engines have about a .2mm shim which won't change the compression all that much given that they're all a fairly low compression to start with. Pinch is highly over-rated and disappears when the engine is turning over fast enough. That speed is about what you can give it by a reasonable flick (so long as there's an oil film between the piston and liner).