Hey all. Well I find that it is the end of my son's baseball season (finally) and time to get some work done on my '57 pickup. I am like most and did not want the gas tank in the cab, but did not want the expense of some aluminum tanks we all see in the mags'. There have been other posts and articles done on under-bed gas tank installs, but i would like to share my experience (plus this is the easisest way to archive and share with friends and family). To begin, I had to choose a gas tank. Now I consider myself rather thrifty (others call me cheap) and this thriftyness would drive me to my choice for a gas tank; 2nd gen. Mustang. I chose a '70 model for its 22 gallon capacity; perfect for a thirsty 406 sbc. The tank is new with sending unit and associated hardware. Cost was ~$130. Next, the most rearward cross member needs to be removed. Do this by drilling and punching out the rivets. I did not want to damage the crossmember because it will be re-used. Next there is a step on the lower edge of the frame that needs to be trimmed to allow the tank to slide between the frame rails. The flange on the gas tank will need to be trimmed to make room for various hardware. In this case, it was trimmed to to clear to bolts for the rear suspension mounts. Pleae note that you must not trim into the pinch weld or the tank will leak. The front of the tank is secured to the shock absorber cross-member (too easy), and the rear must be modified to receive the rear lip of the gas tank. I sectioned the lower half of the raised portion of the cross member to receive a piece of c-channel I had laying around the garage. The following pictures explain better than words. One of the things that I wanted from the beginning of this retro-fit was for the gas filler to be behind the license plate. You know, one of those really cool ones that flips down from a '60s GM sedan. To accomplish that, the top plate of the cross member must be relieved to allow the filler neck to move to the rear between the bed and the top of the gas tank. A notch was cut and piece of 3' tubing (old driveshaft) was installed. Also, blind nuts were added to the cross member ears to allow for "bolt-in" assembly. Final trimming is completed on the gas tank to clear all of the hardware between the frame rails in the tank vicinity. Last j-nuts are added to the tank flange to secure the tank on the front and rear edges. Everything is then put together. I will add to the post later when the filler neck is fabbed and the bed sill is relieved for the gas cap.