66 body to 71 truck frame questions ???

[wahl4m]

im putting my 66 chevy crew cab on a 71 chevy 1 ton chassis mount camper frame . it looks like the 71 mounts are identical ,/except a bigger mount hole ? AND the location is about 1 inch off -front to back ? can anybody confirm this ? i was measuring from the c/line of mount to the back of the front suspension crossmenber ! once i get this measurement confirmed ,i think i will drill and rivet in a set of 66 mounts and locate the rears and rivet them in also! i sold the 71 dually suspension and bolted in 1986 front crossmember and a 86 14 bolt all single wheel stuff ? the rear even bolted down to the 71 center pins,NOW i need to decide what box length to put on it ?? i think a 6 foot might be neat ? probably use this truck for pulling car trailer ? i did see a picture on this site of a similiar truck 3/4 ton with a 8 foot box /in the phoenix area ? anybody know the owner ? thanks mike