Here you go

915 closed chamber, .710-.730 to flat target area next to sparkplug. Lower row of headbolt bosses.955-1.010, this is average of 6 pair of 915 big and small valve heads.

906 open chamber, .729-.735 to flat target next to sparkplug, lower headbolt boss all were 1.00, with my chinese calipers only 4 heads with 1970ish date codes.

Now the real important measurement

Valve tip to outer unmachined valve spring seat area, 2.095-2.135. Stock low mile untouched heads measure 2.110 pretty co sistant. If you want your rocker arm geometry correct, with stock parts this is critical. Measurements are taken from a miller c3648 go no go tool that is mentioned in the service manual.

I have learned after 40 years if I walk in a machine shop to pick up my heads and they say, hey are you going to be running adjustable rocker arms on these? My heads are done wrong, may be ruined but will for sure need more work and $$$$ to fix. Give them a valve stem height that you need as they are not smart enough to measure it before they start.