Well progress, changed the water pump (nowt wrong with the one I took out) so changed the timing belt as a matter of course.
Did away with the swirl pot and reverted to standard hose set up, stuck in 7,8 litres of plain water as bloody coolant stained all the monoblock.
Leaves me thinking was this just an air lock?
Starts and runs fine, fan kicks in and all seems well
However the new sump and gasket pissing oil when hot. Fix that, m.o.t. and the Love affair will end. Stage 3 head and fully recond short
block can go in the boot for it's new owner,lol.