@Ouby I'm pretty sure the pinion gear is integral to the main shaft. You would need the complete shaft.
It is conceivable to be able to do a mash up of ratios from different boxes, until you get a set up that suits.
I am tempted by a 500 box for mine, as they are c-514 boxes and return some impressive long ratios. They are also coming into the realm of affordability.
:O, does that mean swap the gear change mech and it fit the older fire engine?
Ming
Ye, from the pics I can find on the box, all looks the same. I found a sales brochure online from the USA. It gave the ratios, when I worked it all out it ended up at 72mph at 3000 rpm, with my wheels and tyres.
I think you may only have to swap the brackets that hold the gear linkage cables and the clutch arm. Because the gear change mech looks the same.