The way I have always done it was to set the head up with the combustion space facing up and get it level. If the valves have been ground then they should hold water. Screw an old spark plug into the head and snug it tight or you could use some clay to plug the hole. Cut a peice of plexie glass square so it will cover the combustion space. Drill a small hole in the plexie close to the center. Find a syringe that is graduated in CCs. I like to find one that goes up to 100 cc. Use some grease as a sealant around the combustion space and then stick the plexie down on the head making sure to get a seal between the plexie and the head surface. Then fill the syringe with water or colored water if you want and fill the combustion space with water counting the amount of ccs it takes to fill the space. Make sure to get all the air out of the space. If you use 60cc of water to fill the space then it is 60cc.