My memory could be fuzzy,
but i seem to recall that in
1994-1997 Rams
long beds regular cabs had "standard" 36 gallon tanks
Short beds reg cab and 134" wb Club Cab had 26 gallon tanks.
Due to customer demand
sometime about 1998
Dodge came out with what i believe they called a
34 gallon special tank
for 2500/3500 Rams with Cummins or V10
with Club Cab or Quad Cab
134" wb 6.5 foot beds.
So there are three different plastic factory tanks.
IIRC at least one Ram 1500 Club Cab 6.5 bed gasoline Magnum V8 owner bought one of the 1998+ 34 gallon tanks and managed to replace his 26 gallon tank.
After reading his post about it I considered doing it too, and did a salvage yard search for a wrecked 1998+ Ram V10 donor with a 34 gallon tank, but i could not find one close by, and dropped the effort.
Since then Titan Tanks have offered very expensive custom plastic tanks:
https://titanfueltanks.com/?make=dodge-ram&cabstyle=regular&bedstyle=long&s=Search