[sloGMC]

So, I recently acquired a pile of GMC dealer general letters and service letters and ran across this gem. I understand that the vast majority of surviving GMCs have rear leaf suspension, but this is straight from the horse's mouth. Hopefully it clears up this great debate, at least for 1971!
As for Tow hooks on chrome bumper equipped trucks, I saw a dealer letter that, while referring to series 4500 and up, said that dealers can have the factory install Accessories (i.e., non-RPO equipment) using the Special Equipment process. Light duty trucks were covered under the COPO system, so I would speculate that some keen dealers may have used the COPO system to have the factory install tow hooks, which happen to be both an RPO and an Accessory. Seems to be no different than how Camaros were being outfitted with RPO engines not available as an RPO on that model.