Max,
Some more questions/ideas.
1. When you drilled another hole in the crankcase, did you go right through? If so, what will hold the new "spindle pin" in place?
2. Is the crankcase thick enough to tap and thread a stud, in place of the new pin you made? The new stud would be slightly smaller than the spindle and would fit in a coresponding hole drilled in the case cover. The idler gear and spindle would ride on this similar to what you already did?
3. Do you think the area would benefit from an epoxy based metal repair/reinforcement such as Devcon Plastic Steel?
Once again, this is good news and thanks.