My advice is to take measurements of your wheelbase front to back. Measure from the middle of the wheel. Also measure your front and rear axle from brake drum to brake drum. Now head out to your local car lot and take some measurements! It can be that simple!
Once you have an idea of what will fit, spend some time at an auction and pick up something with body damage for cheap!
Don't limit yourself to trucks. Try looking for a car with a frame under it. I'm putting a 1989 chevy Caprice under my 1963 chevy shortbed stepside project. A lot of early american cars from the 60's and even as late as the 80's had full frames under them.
You can obviouly use earlier stuff, but parts are easier to locate for the newer stuff.
