While awaiting the opportunity to make a start on cutting the gears. In spare moments, I have been having a play with the Gear Generator add in, in Fusion 360.

I decided to create myself a working drawing of the Shogun gear replacements that I need and I was quite pleased that Fusion came to the same conclusions about size etc. that helpful fellow modellers (who are far more experienced in the subject than I,) had already worked out.