Dave I am painfully aware of the Hall Hewland box as I stupidly passed on one that PJZ offered for sale. I'm now kicking myself of course.

I haven't done the math on the gear tooth count but if for example 56, 60, 63 series gears fit on any mainshaft one could in theory get the gear tooth count you need on the main shaft then machine the cluster gear accordingly.......I seriously doubt parts are mix and match but one never knows.

Tom