I would remove the pushrods so both valves are shut, install an adapter in the sparkplug hole that allows you to hook it up to air, and put 90 psi or so in the cylinder. The engine will probably rotate as you pressurize the cylinder, this is why you cannot just put it at TDC so both valves are closed, you have to remove the pushrods first. Don't forget to put rags in the oil holes in the head in case you drop a keeper.