Following on from my post regarding the top header tank hose, we came to the conclusion that the top header tank hose needs connecting as high as possible in the coolant system! So with my rad having no bleed and being small, the top
radiator hose ( where it comes out of water outlet cover) is probably the highest point. So could I tee the top header tank
hose to the top radiator hose, as it's the highest point? Cheers

If you fit an expansion tank to the top most point in the system then this tank can be low down, if you look under the bonnet of SD1 rovers you can see this in production cars.

All you need then is a method to fill the system, from the highest point in the system where take a 1/4" pipe to the expansion vessel. This is the only pipe to this, its not a flow through method.

my bleed hose to tank is off of the top hose and it works!

Is this the header tank in question ? it looks like it only has 1 pipe going to it + 1 over flow from where the top fits that top one is only a over flow pipe

It has a large outlet on the bottom, a smaller top outlet and a blow off in the filler neck!