That vintage 454 is TBI with only 230 hp, towing a 4300 lb vehicle would really tax that engine and the rest of the drive train even if you could reweld the frame extensions. They run hot anyways pulling a heavy vehicle will just create more heat. Are the radiator and fan clutch original? At the very minimum I would add Thorley headers, a FF muffler and CAI that will increase your HP to a little over 300 and reduce the number of down shifts on hills which creates more heat in the transmission. You may also need a larger transmission cooler. Look closely at you gvwr and what your MH weighs, you may be close to your limit now. Bottom line I would tow a lighter car.
