Side Mount Fuel Tank Dimensions

[jnocero]

Does anyone have the dimensions of the 16 and 20 gallon side mount fuel tanks?
Is there any chance that one of these could be made to work on a 67 C-10? I want to keep my spare tire under the bed, and get the fuel out of the cab. In the 73-87 photos, it looks like the cab is higher, or the rear cutout is larger for the tank to fit through?
I posted on the 67-72 site, and found that there was an option for extended range saddle tanks, but most rusted out, and good luck finding a set.
If the 73-87 tank won't work, I will try to find a rectangular plastic tank to fit up into the bedside in front of the rear tire.