Leaf or coil standard rear spring on GMC?

[71CHEVYSHORTBED402]

Originally Posted by sloGMC

The service news letter from 1971 is part of a series of communications beginning with the 1969 model year about available suspensions, sagging, and overloading the trucks. There remains no documented evidence that GMC was any different than Chevrolet regarding base equipment -- coils were standard, and leafs were optional. Some literature indicates that both were optional and neither were base. Reality 50 years later makes it appear that most GMCs were made with leaf suspension, but there's at least two explanations at play here:

1) GMC as a brand decided that they wanted more leaf suspensions on dealer lots, so that's what they built and provided to the dealers; the optional leaf suspension

2) Survivorship bias; they fact that more leaf-equipped GMCs exist today does not prove that more existed when they were built or that it was base equipment, merely that more leaf-equipped trucks are still on the road.

Consider the following scenario:

For some reason, 50 years into the future the current K2XX truck platform is super popular. If you were going to infer base equipment on the volume of said option or model, decades after production, you might talk yourself into thinking that the Crew Cab, Short bed, SLT or Denali trim were base equipment, because all the single-cab work truck models have long been scrapped. Obviously that would be an incorrect assessment.

The same argument applies here -- no documentation has ever specified that that leaf springs were base equipment on GMCs, but why it appears that more GMCs were built with the optional leaf suspension, take your guess.

Was 1969 a cutoff point for something? Were all 67-68 GM trucks leaf spring or?