Hmm, well so far in the process:
Deleted the duplicate model, deleted the skin modifier on the one-piece model. Reset X-form. Something happens...
Apparently a bunch of hip bolts have now moved outside the body.
Still though, even I haven't gotten that far, having all the bones in all the skin modifiers... isn't only max 4 bones allowed in each skin modifier? In a previous attempt to make a glm out of it, it told me it couldn't have more than 4 bones in each list. I think also Tim Appleby said that.