i was looking through the BSOC Goldie magazines for info on the BB engines and came across an article in the Sept 2017 issue that included some info on the engine preparation for the 1954 Daytona race. A dyno chart for one of the spare BB34 GS engines shows it was putting out 43.6 hp at 7000 rpm. Not too bad for a BB engine. It might help to explain the Daytona successes.
It also puts into perspective the success of privateers in the TT races who had "borrowed" factory engines.