Hi there, Rebekah & JS,
Oops!!! My mistake!!!
The part numbers I quoted in my earlier post are for the steel gears that the Tufnol ones replace.
The part numbers Mytholmroyd-Myford quote for the Tufnol gears are:
A1781, (B36, Reference Number 498), 18 teeth, £17.68 + VAT.,
A1782, (B35, Reference Number 499), 20 teeth, £17.68 + VAT.,
All the tumbler reverse set-ups I have encountered use two non-identical gears (idlers).
Regarding your point, John, I guess that can only be resolved by a comparison of the gear centre distances and spindle diameters on the ML4 and ML7.
Best regards,
Swarf, Mostly!