I was finally able to break in the new engine with flat tappet cam yesterday.
It was 107F in the Arizona garage and ran the engine at 2000 RPMS for 20 minutes.
The Ron Davis Rad and Header tank conversion held up well. Coolant temps stayed around 200F, measured with infrared gun on the coolant hoses. No boiling over at any time even after shutting the engine off.
I know this will change with conditions and load but feel confident in the cooling system at this point.
Thanks for all the info on the forum to get me to this point.