I know what you mean. I like to keep mine as original as possible too.
I bought mine from the original owner (a 1975 K20) and it came with the jack, wrench and rod. Try LMC Truck Parts, they seem to have a good stock of parts.
You're correct on it being an option in 1975. When I bought my '75, I was very pleased to have the folding back rest. There is considerable storage there as well as under the seat.