Has anybody else spotted the ‘missing’ radiator filler neck and cap ?! (click onto the photo, and as it is a JPG image you can fill your screen with it!). I can only assume that a left-hand filler radiator, of ‘works’ TT type was used, but that doesn’t quite answer the puzzle because, with the bike having a single downtube frame, the radiators used on them have to be the sort with a slot down the middle to accommodate the top hose, which would otherwise foul the downtube. I can only think of those L/H filler radiators fitted on the two 1930 Manx Grand Prix Scotts, that were Sprint Special based, and the epitome of the “Shamateur” early days of the MGP, when bikes were supposed to be privately owned and entered, but most were really ‘works’ bikes supplied to favoured riders such as Mavrogordato and Stobart, complete with works mechanics and covert financial aid too !
All we need now is a L/H side view of one of these machines to see what the description “straight thro exhaust pipe” meant. If it meant no silencer at all, they wouldn’t have needed a siren as you would have heard it coming half a mile away ! If all 35 (?) bikes were running together it would have blown the tiles off the roofs of Buenos Aires !