The symptom you described are that of the air pocket I described. To fill your engine with the funnel (I've used one for years) top off the radiator the best you can and run the engine. As the engine warms up, the anti-freeze will start to rise in the funnel. When it gets about 3/4 full, shut off the engine and let the anti-freeze draw back in. You will also need to add more at this time. Keep doing this a few times until air is out and anti-freeze stops rushing over. I now use a vacuum system that puts a vacuum on the cooling system and draws the anti-freeze in with out air pockets. It will also tell you if you have a leak as in a headgasket. It won't hold a vacuum if there's a leak. Everytime I service my '64 with a 350 in it, I have to purge the air out. Until the thermostat opens and stays open, that air will be trapped. If your head gasket is bad, it shouldn't boil out unless it's very bad. You would smell anti-freeze at the tailpipe and the system would be under high pressure as soon as you capped it. You might still have a gasket problem, but it would be more of a light stream of bubbles at an idle.
Just some food for thought,
Scott
