World product S/R head milling

[Fastbydesign]

I have a set of World S/R heads for a small block Chevy. Currently 68 cc chambers. I want to mill to 63 cc for class rules minimum combustion chamber. World says flat mill .0065" per cc. I need to mill .032" to remove 5 cc of volume. World says .020 max flat mill. Does anyone have experience flat milling these heads .032 (or more)?
Thanks

[Newold1]

It does not make a lot of clear sense why an extra .012" would make that big if a difference unless the intake valve seat edge is already close to the heads flat deck surface. If not I don't see how that extra small thickness would cause a problem with the head. Intake might need a little milling for fitment and alignment.

If your valves now have concave recesses in the faces you could switch over to valves with flat faces as this will remove some addtional cc"s.

[Keith Morganstein]

I've flat milled .060" off those heads and angle milled them .125", no problem.

[Fastbydesign]

Thank You for the information.