Interesting that they used a synchromesh gearbox back then, I thought the later Ergomatic cabbed Marshall’s had a constant mesh one? Back in the sixties we used to service a Mustang owned by Gillette Industries, I assume they were similar mechanically to those in the brochures? I seem to remember it having the aircleaner in the cab though, and the little red ‘flags’ that popped up to let you know that you had now no brakes! 
Pete.