Lots of good advice here. Morris Oils good. Fuzz Townsend's company, Classic Car Oils at Bicester Heritage are also very knowledgeable. They produce a 20/50 with high zinc content similar to Valvoline VR 20/50 which I use for the Plus 8. Widely used by Mog Sport racers for the Rover V8.
https://www.classic-oils.net/MobileSubCat.php?MainCatID=280
