I removed my under bed fuel tank from my 47-48 3/4 ton. It is not like what is pictured available in the after market parts suppliers. It measures 7 1/4" deep x 12" wide and 41" long. It is supported from two brackets that are riveted to the frame and straps that go under it from the frame to the end of the bracket by the drive shaft side. The fill spout is located on the top near the rear and the gauge sending unit is also on the top just in front of the fill spout. The cross sills are way above and do not come anywhere close enough to the tank for any interference. Is there anyone that reproduces the proper tank for the 47-48 under bed tanks? I can repair my tank (dents) but I would consider a new one if it was available.
That tank is not available anywhere. I found a good used one for my 3/4 ton, had the outside sand blasted and I sealed it with POR15 tank sealer, and the inside as well. I'm keeping my eyes open for a spare just in case. If you decide not to use that tank, let me know.
I second what RyanC said, the tanks are not reproduced. I put a generic one in my 48 3600, between the back of the cab and the next cross member. if you do some searching, and have some fab/welding skills, it isn't a huge obstacle.