Back in the late 70s, I owned a 70 Mach 1 that was equipped with a trailer hitch. It was fairly light duty looking, it had a large H shaped bracket that attatched to the rear bumper with 1 bolt per side, and a middle member that held the hitch ball, and ran under the gas tank, and up to the floor pan between the rear shock upper mounts, ahead of the gas tank. I recall seeing a fair number of similar hitches on Mustangs around that time. Pretty light duty, but I did tow a utility trailer with a 428 I had bought, in it thru a few towns without incident. You will be towing much further, but likely with much less weight. Does your Mustang have a fold down rear seat? For years I drove my street/strip 69 & 70 Mustangs to and from the dragstrip with 1 slick on the fold down seat, with other in the trunk (8 1/2x26-15, or 10 x28-15), and a tool box and small floor jack in the trunk.