There were two Commandos built for the 1967 Earl's Court show. Both were fastbacks, the only version we had at the time. They were finished in Silver paint (tanks and frames) with orange seats and the dreaded "Green Globe" badges. One magazine "wag" suggested they'd been commissioned by the Irish government, as they had the three colors of their flag (well, silver rather than white). Someone visiting the stand asked why the turn signals were green.
I was on the stand at that show and was particularly embarassed by the awful scooter we showed. It was a product of Villiers India and (believe it or not) was called the "Fantabulous". Originally, the prototype came from India with a kick-started 175 engine. We modified it to take the 197cc "9E" electric start engine. It was still an unstable POS. While my 650SS was back at Plumstead for development testing, I rode the scooter to and from home. Scary as hell - directionally unstable, skinny tires and a structural configuration that still blows my mind today.
I'm not sure how to identify a 1967 engine. I'm pretty sure all the production bikes would have been designated 1968. We had just two protoypes with fuel tanks that looked nothing like the final version and they didn't have any of the production bodywork. They also had speedometers that read 1.6x actual speed and no stands (either center or prop). We had to find a tree or a lamp-post to lean them against when we stopped out on the road. I'm not sure if the two show-stand bikes were the prototypes tarted up to be on the stand. Memory is none too reliable, but I'm not sure we did any more testing at Marston Road after the '67 show. I certaily don't remember testing anything with the fastback bodywork. We'd moved on to the Stormer program by then.
Maybe Plumstead production test did some mileage on the two show bikes. Member Norton-Villier might know, as he was at Plustead during that period.
Rachel - It's not clear from your post whether you have a complete bike or just the engine and gearbox. Please clarify.