I think you are right with the 1:00 cam, 7:00 crank and use a straight edge to check centered on the shafts. Don't worry where the piston is. Then check where the cam lobes are when a piston is at TDC. Put the piston at TDC on the exhaust stroke and the lobes should be pushing both valves somewhat (valve overlap). Rock the piston forward and backward to see if the lobes are more or less centered and both valves are open the same amount at TDC exhaust stroke.