x2 on ASU. Mine is a 41 3/4 ton, but the frame rails probably measure pretty close to the same: somewhere around 33" as I recall. You will be sacrificing capacity, however. Nowhere near your desire of 34 gallons. I think it's around 12.

~ Victor
1941 3/4-Ton Pickup (in process). Read about it in the DITY Gallery
1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD
1957 3100 - moved on
1959 C4500 Short Bus "Magic Bus" - moved on
1959 G3800 1 Ton Dually "Chief" - moved on
1958 C4400 Viking "Thor" ~ moved on to fellow Bolter