If you are going to continue with the leaf springs on the rear, you really don't need to do anything to that car except attack the lower traction bar to a spot thats about a foot in front of the leaf spring front hanger--In 1964 I raced a cyclone and I ran a piece of angle iron along that lowerportion of the unistructure to the mounting point

Now, if you are going to add coil overs you will need toadd strength to the upper mounting area to carry the weight ---back in those days they were running the AF/X cars with pretty much just a cross member mount in that area for the arms to hook to.

Your biggest area to work with is the front suspension on that car to make room widthwise for the engine/exhaust