Big air lock there. Fill to brim with engine off put your hand over the top and squeeze/pump the top pipe coming from the pump. Keep toping up and repeat. Might take a fhew times. Then when your happy keep toping up slowly noteing any air coming from the small return pipe at the header tank. When thats all done give both top hoses a good squeese to lower the header tank level. Then cap on and run at a fast idle until nice and hot and squeeze the pipe from pump to rad to shove the water around. Use a cloth. Let it then cool and check level. Hope this workes for you as it does for me
I am hoping it will still work when I've got it back together and I can remember where all the bits go. There's a bracket underneath somewhere that holds the loom but damned if I can remember where it goes. I'm hoping the bolt holes (and indeed bolts) will become obvious once the gearbox is back on!