This is about the only pic I could find that shows my header tank setup.
There's an AN#6 fitting I've silver soldered onto the crossover pipe between the heads. This leads to the top of the header tank to purge any air bubbles out of the system. There's a similar AN#6 line from the top of the radiator to the top of the header tank to burp the air out of the radiator. The line at the bottom of the header tank is an AN#10 and it runs to halfway up the radiator side tank. This is the fill line. The radiator and engine block fill fine, you just pour the coolant straight into the header tank and it drains through. Air is purged out as you go. I've had no overheating problems and the temp guage has behaved itself even on the track.
I've still got to make a matching overflow bottle.
Cheers