NickD,
I feel for you bud.
It sounds to me like you are getting combustion gas into the cooling system. This might not be a head gasket. It might be a pin-hole leak from the exhaust port to a water jacket. One of the guys on the 3Geez forum talks about hitting water several times while learning to port and polish Honda heads.
I'd recommend draining the coolant, and then use an air compressor to pressurize the cooling system with air. Take the exhaust headers off, and listen at the exhaust ports for air hissing out. Spray soapy water to see if you get bubbles.
Then, you can remove the spark plugs, and listen at the spark plug holes. That will tell you if you have a leaky head gasket.
Be careful when you use air pressure to check for leaks... If you pressurize the cylinders, then the crank will turn. If you happen to have your fingers near a fan belt, you might lose them.
Cap