Finally got the pump off (well, my welder did!) and took it to a local 'reliable' engineer
Water Pumps - Vintage, Veteran & Classic Water Pumps - UK
Cost £200 plus Vat but he had a lot of trouble getting the pully and impeller of. He said Bristol were very thorough!
The old bearing is hand pressure seized.
The offending top bolt was virtually seized into the block by corrosion. Now to refit with new ss bolts and plenty of anti corrosion fluid. A non standard part are studs in place of the two lower bolts with W/W nuts.