That oil was one of about 50 that Jim Comstock, the Norton guru, tested in his scar tester.
It did very well at 337 lbs load to failure, and it's not expensive.
150 lbs at load failure was considered minimum acceptable for a stock engine.
Some of the very expensive oils turned to smoke very quickly. Redline 20/50 Synthetic with its very high Zddp of 2200 ppm failed at 119 lbs. Shell Aero Aircraft motor oil for flat tappet type engines sounded promising. It turned to smoke as soon as the first weight was added to the load arm.
96 lbs was all it managed.
I haven't been able to find the Castrol Classic here in Canada. Too bad, as the 337 lb load at failure puts it near top of class, recommended for Stage 3, Full Race engines.
The tables listed a number of oils with load ratings in the stock engine group, from 150 lbs to 175 lbs at failure.
Next was Stage 1 performance at 175 to 200lbs, Stage 2 at 200 to 300 and Stage 3, oil for full race engines at above 300lbs. Heat from friction was also measured.
Royal Purple HPS 20/50 (437lbs) also scored extremely high and it is readily available here. It showed negligible heat from friction.
Valvoline VR1 20/50 handled a fairly high load , just into Stage 1,(205 lbs)before failure . The straight 50 did even better at 230 pounds The VR1 is a conventional oil and not low friction like the HPS. A higher friction oil could be a good thing for a Vincent, especially in cool climates. As we know, Vincents take a long time to get the oil up to a good operating temp.
VR1 is one of the easiest to find here on the West Coast of North America, US or Canada.
Its probably not available in the UK, however you have the Castrol Classic which is all you really need.
Brad Penn Penngrade 1 20/50 was the only Brad Penn oil tested. It had load failure at 152lbs. It had very high heat from friction.
Glen
