I have bought over a dozen Spectra Premium tanks over the years for my GMCs as well as my Y-Blocks and I am convinced they are the best one can buy for gas, but I would be hesitant to put Diesel in them because they sure look galvanized. I don't think the originals were galvanized, in fact I have thrown quite a few that were probably still good simply because for less than $175 for a new one, I didn't want to mess with an old one. My 520 gas burner came with a square tank.

https://plus.google.com/u/0/1126369...3154546690&oid=112636930370126476644

I just cut the draw pipe off a couple of inches to stay away from the dirt a little more. On a diesel, I would put the draw on one end and the return on the other end to stay away from the turbulence of the return. The absolute best for Diesel is aluminum. If you are looking for a square one, I have seen them on eBay. I think they are for boats, but what works,works. Just fill the tank with nitrogen and weld in a return.