I think the reference to the pre 73 frame was referring to replacing the whole front frame section from the firewall forward and removing your present front section. I' ve done that using a 1980 1/2 ton front frame clip and grafted it to my 58 gmc frame. The frame width and dimension is the same. With the steering box on the outside of the frame it's easy to build mounts for your rad core support too. If you need to add 2 inches it might be just as easy to change the front frame out. JMHO
