Pretty much sums it up. Measure, measure again, don't forget to figure in the head gasket thickness. Measure again just to make sure you are right. Have way to the machine shop, turn around to go home and measure again. When you get to the machine shop, have the machinist measure it a few times for himself. Corroborate between yourself and the machinist a couple times including measurements. After he sets up his machine, he measures a couple times.
After you get the heads back in your possession, you put the motor together with an old set of head gaskets and some putty on top of the pistons. Bar the motor over a couple times to make sure everything clears. remove heads, measure clearance marks on putty, allow a .001 for new gaskets and .0005 for expansion. If the clearance looks good, throw it together, get it warm and try to break it.
