The second problem in making the Mustang tank fit between the framerails, is that the inside of the framerails themselves need to be trimmed. The truck's frame measured 34 inches outside to outside and 29 1/2 inches from the inside edges side to side. Since the tank body is 30 inches wide, I needed to trim the inside edge of the framerails a little so the tank would fit flush and tight on its flange and not hang down too far. I used masking tape and scribed a line 3/8-inch on the tape on both sides of the frame (3/8-inch was just right, a 1/4-inch just didn't do the job). My trusty Sawzall made short work of the trim line, and I dressed the cut with my trusty old right-angle grinder.