The first place to look is the inside the door on left side. If not there you will have to climb under the truck on the right side about the center of the frame on the inside of the frame rail. If there is a lot of rust that place might be gone. The last place to look is the fender next to the firewall sometimes they placed a number tag there on a bolt. As last result go to the local ford dealer and have them run the serial number off the engine block. Good luck...Doc......