When my 100/7 destroyed it's gearbox I used an 82 box as a doner. The input shaft is longer on the 100/7 so you will need to change that to allow the clutch to operate. you will also need to change the output end cover so that the correct length push rod can be used.
It's not quite as simple as simply swapping the input shafts because the 100/7 gearbox uses input gears with a 15° angle (17.5↑8) on the later gearboxes. The later gearbox also uses thicker gears. The only solution is to swap all the gearbox components over. Which ever way you do it the gearboxe need rebuilding.
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