New modified top bearing housing fitted and seems to hold firm. Will have to have it running to see if long term fix. Shimmed bevel gears fitted springs valves etc. Nipped up head bolts Checked piston / valves and and head clearance all good. Cleaned everything and refitted head. as I was torqueing head bolts engine started to get stiff to turn but not locked solid. Removed and checked everything to try and find what I had done wrong, Unable to find anything, all revolving OK. Reassembled very carefully, started binding again as I put about 15 ft lbs torque. What a puzzle. The only thing to come in contact is the new Oldham coupling. Stripped again, Coupling good light fit on shafts, I still had old coupling and measured lengths. New coupling is 0.60mm longer than old one and was binding on shaft circlips and, I think, pushing bearing inner against balls and making bearing and gears bind.
Altered length of new coupling and assembled again. Torqued to 25 ft lbs no binding.

This engine is certainly giving me lot's to think about.
Right side oil pump and points fitted . Points set up, valve timing checked to make sure my refurbished cam is correct sport cam. Valve timing is as per manual. Clutch cover fitted and oil added.
Question: Is there any way I can check oil is circulating with engine on bench. I don't suppose turning over with kickstart will get oil up to camshaft but I would like to check somehow before fitting. Any suggestions welcome.