I'm not warning you that it will be messy - just that at $25.00 a pop, removing the head gets expensive. I just tried two different heads on my B18B before returning the original and the cost in finding and replacing gaskets adds up. Remember that you should never re-use a head gasket.

If you've had the head off a few times... well it's possible that you could have a trapped air-pocket. Removing the the temp sender, being at the back of the head, will allow you to check and see if it is full of coolant, and would allow excess air to burp out - if you've got a lot of air in there. Easy check costs nothing if you are careful.

You do have approx. 2 gallons of 50/50 in there? The first time I performed a complete engine swap I managed to blow out my head gasket and probably burned my #7 valve because I could not get the full 2 gallons of coolant in there. Chalk it up to my own ignorance.

Hang on... is this a B20? Has hot running been an issue before?

Others will chime in on this, but I'm not sure that the B20 should be run with the open cooling system... You do not have an overflow reservoir setup?

You might want to check out Ron Kwas' site at sw-em.com He has something on radiators...
Actually I don't see it... oh here
http://www.sw-em.com/service%20notes.htm#Cooling%20System

Try VClassics also