I gave up trying to understand the haphazard way in which BSA delivered the change over to unified fasteners. The 5/16" rocker cover studs are unified, but the 1/4" are CEI, on the same head casting!?!
The carb studs remained 5/16” BSF/CEI also
Tell me about it! I had to order new CEI
allen bolts to mount the Mikuni adapters because they came with Triumph bolts, which were UNF
New head casting for '71 but they couldn't complete the change to unified.
Too many old bits around? Easy solution, ship them out as spares and charge twice as much for them.