NAPA sells a "block test" device that checks for combustion gases in the cooling system. It consists of a rubber squeeze bulb that draws up gases from the radiator through a blue liquid that you pour into a reservoir. If a little exhaust gas is present, the liquid turns yellow. A bad leak turns it green. I use one of these testers frequently, but if you don't want to buy ir fot a one-time use, most good auto shops will have one and they can do the trest dor a small service charge. O'Reilly's sells an identical-looking kit, but for some reason, the NAPA test fluid works better.
You could also isolate the engine from the rest of the cooling system by using two long flexible radiator hoses coupled together and applying air pressure to the cooling system after filling the engine with water. If you put much pressure to the radiator and/or heater core, you'll create leaks. If the air pressure drops, remove the spark plugs and spin the engine with the starter. Coolant will squirt out of whichever cylinder has the leaky head gasket or a crached head.
Jerry
