Another mechanic screws me over.....

['63GENIII]

That whole deal sounds like it sucked. Im sorry to hear this happens to anyone. Moving ahead though, you're in the right place to get her put back together and you're getting a lot of good suggestions. I did notice that you seem to be missing a rear crossmember? Im a K series guy so I don't know much about the differences between the C and K frames and if there is one there to begin with, but the 4x4 frames have a rear crossmember that I had to remove when I installed my Blazer tank. I installed a new one fabbed out of some 2"x4"x1/8 tubing and welded a couple of 3"x3" angles to keep the tank from going above the rails into the sills. This tank would hang way too low for you but the principal is the same. Stock Blazer tank straps on the bottom too (just shortened a little). Oh and the filler does fit in between the bed and the frame due to the angle. The fuel hose is a good idea. You could also find some metal filler pipe (from a wrecker) of different angles and attach with short pieces of the fuel hose.