The CR A65 box has RPM drops of 2065, 1854 and 725 RPM @7500. The ratios I am using are 2564, 1670, 1041 and 725 RPM which I think is what you want.
With a fixed centre distance and changing ratios the pitch has to be modified since a diametric pitch and number of teeth determine the pitch circle. I was able to get all but one gear set in a standard pitch diameter.
Possibly Quaife did not want to change ratios because it would also entail changing the forks to clear the adjacent gears. When I had drawn the shift plate version I had the second and third gears swapped from where Quaife put them and moved two forks for second rather than a single fork which gave more room in other areas.
The reason to go to the drum was the awful ramp required for first with that track being so close to the pivot point.
At this point you have to tune the engine for the gears that you have rather than design the gearbox for the engine power curve.