if you look at the bottom of the head, there should be a triangular area at the center of the head and to the pass side (I think) and also at one corner that would still have that rough sand casting look. If these are not there, then you have definitely had alot taken off that head.
Do you have another head to compare it to?
What are you going to use for a camshaft?
You should try to keep around 0.090" clearance between the piston and the intake valve. It may be necessary for you to put it together with some clay on the top of the piston and roll it over and then take it apart to see what you really have for clearance. You could reuse an old head gasket for this purpose, but only if it is the same as what you will be using in the end, as the newer style gaskets are a bit thinner than the original ones.
If you find that you don't have enough clearance, then you have 3 choices, cam with less lift, recess the intake valve or mill some clearance in the piston.
When large amounts are removed from the head, that lowers the centerline of the rocker shaft. Moving the intake valve up higher into the head makes it even worse. Since shorter pushrods aren't available, you need to shim the rocker stands back up to try to get the geometry back to "normal". Just backing off the adjuster is not good enough, because the cup on the pushrod may bind up on the adjuster/rocker arm if the changes are significant enough.
There is a "window" where the tip of the valves, the center of the rocker arm, and the and of the pushrod need to be in order to function properly.
