Jimmy/Burb sending unit differences? Lengths?

[87R10]

I'm trying to find a sending unit for a custom tank I'm making. My parts dealer says the 40 gal Burb unit is worth $300 LESS than the Jimmy's 25gal tank unit. Is there a different lengths? (Deeper tanks? I just assumed they were longer tanks, not deeper)

 

[crazy4offroad]

Yes they are deeper, but I cant tell you exactly how much. There's a 25 gallon Blazer tank, 30 gallon Blazer tank, and the 40 gallon burb tank. Between the 25 and 40 gallon tanks there could be 3" or more of difference in depth. I think the only difference between the 25 and 30 is the bevelled cleft in the rear of the tank of the 25 gallon, and it isnt there on the 30 gallon, more squared out.