How do you stop triumph stag v8 engine overheating?

Are you asking about the Triumph V-8 or a conversion V-8? Had two Stags converted to

Rover/Buick V-8s. Easiest thing to keep from overheating was not to use a cross flow radiator. If you use a cross flow, you will end up with a air pocket in the engine. You can get a header tank off a TR-7 or TR-8 and take a tap off the top of the intake manifold. Need to put the tank higher than the engine.