When I had my Cobra, one of the tricks used was to jack the rear of the car up as high as possible allowing any bubbles to move (hopefully) up to the expansion tank. In my beast I had a Transit diesel Rad but you have to realise that, believe it or not the V8 doesnt get very hot.
In my Morgan replica I am building at the moment it has an RV8 in it and I have fitted and MGBV8 Rad in it

Hi Ian.

I just had a thought - I don't know if it's worth trying! A fairly recent development in the 'additive' market is radiator water 'wetting' agent such as Miller's Rad Hib Extra Cool stuff.

I understand it works by breaking the 'surface tension' of water (a bit like adding detergent to a pond and watching the 'Pond Skaters' sink...), which gives the water better contact with surfaces thereby aiding heat transfer. I'm actually thinking it might also in your case make any air bubbles less likely to 'stick together' forming air-locks, and more likely to 'creep' along the sides of the pipes and make their exit! With less surface tension, the air bubbles should break up into smaller ones, and could even be carried out by the water flow until they can exit the way they should!

(If you imagine a drop of water sitting on a water-resistant surface, it'll form a 'bubble' with only a small contact area underneath on the surface. Add detergent, and the water's surface tension is removed and the drop will spread out and flow out. It's been made 'wetter'!)

I've no idea if it would work this way, but it might!