That's right, 'they' seem to love hacking off the frame lug at the rear of the primary chaincase which would normally be for the inner primary case fixing point, to clear the longer Triumph case. It can easily be weld repaired though. Some nutcase had swopped a Goldie engine for a rattly Triumph lump before I got it into my hands. No other problems though, but lots of bits had to be located. Lyford Classics, Cake Street Classics and George Prew come to mind for bits, but you will likely have to trawl ebay for bigger bits. Primary cases and gearboxes come up surprisingly often. We mostly like to use the Triumph 4 spring clutch so you may already have it on your Tribsa and need to only change the hub adaptor to the BSA type with a spiral extension to assist oil retention in the case.
Good luck with your BSA rescue.
Alan
