Well, even if you took a dial indicator and modified it to screw into the head it would only tell you the stroke, position of TDC and BDC etc. To get actual head clearance it would have to have some sort of arm to go up against the underside of the head to measure from and such an arm would not fit through the hole. Maybe there is some way to do it but I can't think of it. Seems to me the old solder trick is much easier and cheaper.