My truck is Factory 16.5 i have pics and i run 35 12.50 16.5 bfg mud terrains on my truck.
cucv trucks are also 16.5 so fyi it is a factory option. k20's and k30s had em as well as the k30 cucv's.
oh and dont try to shimmy a 16 inch rim on a k20 or cucv because it will rub the caliper...