Loz the carbs we fitted the powerjets to were 36mm. not stock
the pipes we made were copies of the factory OW70, the owner had a Yamaha book choke full of engine specs for the '83 GP model and the engine was built along identical specs from the base gaskets up. Problem was in this application the motors pretty much run either flat out or nothing but it proved pretty reliable. Blissfully unaware of problems yes
had a few little teething problems with the rear cylinders leaning out /seizing but this was overcome after about 4 meetings ending in DNF's
Seems the only pics I have showing the beast without the bodywork is a video..VHS though..