[Jac Mac]

Mando, The majority of coolant flow in a Ford is In @ front of the cyl block, up thru the large transfer openings at the rear of block/heads, then forward thru cyl heads to Exit at front---- to provide a rear exit as you have there reduces the amount of coolant available to cool the cylinder heads.

By taking your heater feed from the 'New,yet to be fitted T/Stat housing or that Housing with rad cap' you will be taking an equal amount of coolant from both banks ensuring that flow remains even.

Seems to be a small server problem @ moment & cannot view your gallery pics. Will try later & draw up a diagram to post tonite.