Rough math says a 0.037” cut on the 113 heads will give about a 6.7cc reduction.  I can’t tell you what this would do to your compression ratio without knowing the specifics on your combination.  Ie. Bore, stroke, deck clearance, head gasket, etc.

A a rule, I try to limit the cut on posted Y heads to a maximum of 0.055”.  Of course this limitation is with compression ratios of up to 13.0:1 in mind so if running a compression ratio much lower than this, then another 0.010” of cut would potentially be possible.  As an alternative, cut as much off of the block deck as possible which will also help to maximize piston quench.  This would minimize the amount that must come off of the heads to get to the desired compression ratio.

With milled heads in mind, piston to valve clearance with stock sized G or 113 valves and camshafts that have an advertised 0.500” lift or less and ground on 112° lobe centers typically do not require any piston notching or modifications to the pistons themselves.  Check clearances anyhow as variances can step up to bite you.  Going to a larger sized intake valve and/or decreasing the camshaft lobe centerline while maintaining the same valve lift characteristics will create a scenario in which valve to piston clearance will need to be checked with much more scrutiny.  When checking valve to piston clearance, also check the intake valve to edge of bore clearance as this becomes an issue at lifts approaching 0.540” and more.