Do a cylinder leakdown test instead of a compression check. With both valves closed on each cylinder, apply 60-70 PSI to the cylinder through the spark plug hole, and lock the crankshaft by putting the transmission into high gear and setting the parking brake and/or chocking the wheels. If a pressure leak is present, you should see bubbles in the radiator. A leak from an oil passage to the cooling system won't show up that way, however.
Jerry
