Quick question is the tank from a 1500 reg cab short bed the same (size and shape) and a 1500 ext cab short bed?
And are all 2nd gen year's tanks the same?

 

Should be. SWB half tons had 26 gallon tanks. LWB half tons had 35 gallon tanks.

OH yeah, SWB 3/4 tons had 34 gallon tanks.

 

But short bed half tons had 26 gallon tanks no matter the cab size?

The only reason I'm asking is for my RCSB cummins, every other build I found says the person bought a 1500 gas tank from a short bed and used their diesel sending unit. So I bought a tank from a 1500 reg cab short bed and my sending unit seems to be about a 1/2" too big and it bottoms out in the tank.

 

Short bed half tons had 26, regardless. (kinda stupid if you ask me)

Maybe your sending unit is from a different year? I dunno about that stuff.

Since you are using a gasser tank, MAKE SURE you clean it out VERY well. Gasoline is a solvent, diesel is an oil, as you well know.