The first problem we encountered was that the new Mustang tank filler neck is slanted. Because the frame is longer in the older trucks, this doesn't seem to be such a big problem. But for our later-model trucks, it is. I chose to mount the filler cap in a vertical position at the rear of the bed floor so the neck angle had to change. I had to cut the original filler neck off close to flush before I could weld a piece of muffler tubing back in a vertical orientation.