Just got a good used head for my 1954 308 Hornet my car has 1/2" head bolts is there a special way or size to drill the factory size cylinder head with 7/16".
So do I just drill all to 1/2" or 1/2" in center 3 and slightly larger going to out side in small steps. Going to have it planed as well how much should be taken off I am replaceing a aluminum head with the cast. I was told my engine has been modified so if .030 is taken of would that be close to the aluminum.
Yes, the three center holes across should be drilled about .505". A standard 1/2" drill will actually drill the hole about .003 to .005" over.Tthe two sets of three holes across on either side of center should be drilled 1/32" over or .17/32", the last two rows of three at the ends should be drilled at least 35/64". this allows for the head expansion when it heats up.
If all off the holes were to be right at .500" , your would have trouble getting the bolts or studs in with a cold engine. With the head bolted down, the expansion of the head against bolts at the ends could cause the head gasket surface to bow upwards, with possible loss of head gasket sealing, either compression or coolant, or both. In my case, when I years ago naively installed a head that I had enlargened all the holes to 1/2", the coolant started seeping \out the sides of the head gasket near the ends. I ended up pulling the head again and re-drilling the holes oversized towards the ends as outlined in above paragraph. The coolant seepage went away.
If you intend to drill those holes in the head, you MUST do this on a BRIDGEPORT type mill. That is the only way to locate the holes accurately and get the drill perpendicular to the head. Attempting to hand drill those hole with a hand drill is asking for trouble and possibly personal injury. I clamped the head on top of parallel blocks on the mill table so it couldn't move. 
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