Hi Drew,
There is the Type 91 MT nose fuze, as you have seen as a cutaway with the gear ring for automatic setting device, than there is the Type 91 without gear ring, than the type "0" for 12 & 20cm projos (outer appearance is the same as the Type 91, except the base assembly looks different) and there is the type 98 MT fuze with a longer cap and gear ring.
Mrfuze, USA