Yes, a little bit of research and the 'missing' teeth are indeed supposed to be missing. Still looks odd!
I do not actually intend to use these chainwheels as they weigh a ton and they will be tricky to fit them to the intended bike.
I plan to use 44T and 36T alloy chainwheels with a conventional five arm spider, should be straight forward I think. I am sort of going for the Bobby Encinas look without the DX cranks unless someone wants to donate a set of those, they are not worth much, no one wants them, honest.
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Simon, regarding the rear derailleur, or more correctly rear chain tensioner: there is no need for a drilling. The bolt you see actually mates to a semi circular boss which locates into the wheel spindle slot, fortunately I have this spacer.
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I have all the parts required except a cable but that will be easy enough to make.