Matt D,
Most older cars, 65 Mustangs included, have shims between the upper control arms and the frame. The shims are largely universal, and are used to adjust both camber and caster for the front end alignment. The shims come in different thicknesses and they can be stacked to achieve the required thickness. You can get them from any alignment shop or mail ordered from a host of places including JC Whitney. The catch is that after replacing (or just reinstalling) all the front end pieces on the car, you need a front end alignment anyway, and the alignment shop will provide the required shims for you.
Hope that helps,
Ron Lee