i don't really think there is going to be a weak link in the hub and rotor assembly, I'm not sure about the caliper parts but the more i think about it the machine shop probably just didn't want to have anything to do it. the guy i had make the adapters said there shouldn't be any problems, he owns a drive shaft/fabrication shop and has built a few trucks. do you think the hub would break with the power of the disks?
