George the frame you need for your car will be found under a 1967-70 full size (aka B-body) excluding the station wagon. The holes or brackets to mount the body to the frame differ by model (Convertible is different from the Hard Top in having an extra cross-member and a deeper, stronger (thicker metal) frame but it will fit under the hard top. The Sedan differs from the hard top as well and all two doors differ from the four doors by virtue of having a different wheel base.
The difference in the 1965 through 1970 frames and the 1971-76 frames lies in how the rear end is attached. In the earlier cars the rear control arms where all parallel to each other and the rear was centered by a Panhard bar that had a bracket welded onto the frame to secure it. From 1971 and up the rear end was centered by means of triangulated top control arms and lower control arms that remained parallel (like what a Chevelle used).
All B-bodies from 1965 up shared suspension parts with the each other and the Corvette (even using some parts off a light pick-up truck). If you are just looking for disc brakes or stiffer stronger suspension parts I would retain your frame and use other parts.