Chazz it's only a suggestion

Viper - The layout has a rad at the highest point in the system!
Turning the Top rad around will certainly improve things, but it will not prevent your Top rad acting as an air-trap.
This could be solved by raising the water level of the pump/res.
By having a res at the top (of the case p'raps ) this will also provide an ideal bleed/refill point. You can also visually monitor your water level in this way.
Yeah I know it's not a dual set-up but I fink it explains what I'mm gettin @
IMHO A simple yet very effective design "tweak" - to actively remove air bubbles in the top Rad.
(the last place U want 'em)
Hope that's helpfull
Mat