A subframe is the front frame stub on a unibody car that the suspension, engine, transmission, body, etc bolts to. Unlike a full frame car, a unibody relies on the body of the car (ie. reinforced sheetmetal) to link the front subframe to the rear subframe. Some hot rodders cut the existing front suspension off of their full frame vehicle(non unibody) and weld on a subframe from another vehicle (camaro,etc.) In your truck's case, you could take a 70's camaro subrame, cut the front of your existing frame off and weld the camaro front end to your 1955 frame. This would gain you independent suspension, V-8 motor mounts, transmision mounts, and probably a lower ride height. It's a lot work and it can yeild unpredictable results if it is not done with a lot of carefull measurements and competant welding.
