Just wondering, would it be acceptable to use a thick grade 8 flat washer under the nut to get the hole/cotter pin to line up with the slots in the castle nut?
Or even a thin grade 8 if that’s all you need to line them up?
I think a washer would be fine, if the nut is so low that the cotter pin can't block it from turning. That solves the cotter pin problem, but not the squashed dust boot problem.