Gear ratios for the 2nd stage of the overall drive ratio.
The center to center distance for the gearbox is 1.803", which is a 72T distance. This means that any gear set that adds up to 72T will fit. The only limit to this is the center gear, which cannot be any larger than 62T, otherwise it will collide with the 1-1/8" Spacers.
Just by going one size larger to a 64T Gear will cause the gear to collide with the spacers.