Measured from the bottom of the passenger side rear stake pocket [to which the brackets in question are attached].
Back Up Light bracket: lower edge starts at 2-1/2'' high.
Taillight bracket: lower edge starts at 6-3/16'' up. This bracket has a half-rolled top edge.
Fasteners are diagonally mounted. Looks like the pieces are pre-drilled in my 10 year old LMC catalog. Don't buy from them much anymore, but their catalog is a handy work of reference.
Taillight brackets differ by Left and Right.
Back Up light brackets are same part for either side. This would not matter if the OEM ''Bullseye" style reverse light lenses were still available, but with the lateral-ribbed lenses offered by the aftermarket vendors, [really '60-'66 types] one looks askew at about 45* if you use the provided holes. It's the passenger's side with the wrong holes. [RH] Personally I don't care, and if anyone says anything, I say the truck ''was built in the late afternoon on a Friday during hunting season.'' That usually shuts them up.
Of course the repop tail light brackets may be drilled to accomodate the aftermarket lenses.
I was looking at my '68 Chevy C/10 shortbed [115'' wheelbase] for reference. I don't believe there was any deviation in the whole series.
Not sure about the longbeds.
