Have your buddy/or you check out this site at GM Heritage:
https://www.gmheritagecenter.com/doc...olet-Truck.pdf
On page 7 it shows Designation “OC412…” as Series C4102 then you can look at page 11 & 25 for load capacity, weight distribution, etc. Should help get some facts about it. Thanks for the photo it looks like an interesting build!