I'm really curious about the cadillac pulling the trailer. How well did it work? Are there improvements you could make to use it regularly? For that matter, has anyone ever towed with any of the 70's muscle cars?
The Cadillac (Eldorado) of the 1970s (through 1978) was generally rated for a maximum of 6,000 pounds towing. This is the case with my '75 Eldorado convertible. The limiting factor is the final drive ratio at approximately 2.70; and as a complex front wheel drive vehicle, changing the final drive ratio is expensive but not impossible. The drivetrain is basically very similar to that used in similar vintage GMC motorhomes. With the Overlander, the Cadillac has adequate power except on steep grades; and it does struggle to get started on even modest grades when the pavement is wet as the front wheels try to break loose before they gain traction.
The following modifications have been required to make my Eldorado an acceptable trailer towing vehicle: new heavy duty four-core radiator, new heavy duty (12,000 pound) rated auxilliary transmission fluid cooler, new heavy duty water pump, new heavy duty alternator, new heavy duty mechanical fuel pump, new heavy duty heat shielded starter, new heavy duty cargo coil springs (rear), new Air Lift air bags in rear springs, new heavy duty shocks (front and rear with air ride control in rear), custom fabricated Reese Receiver Hitch, new custom wheels (finding unbent, ture-running originals proved nearly impossible - - the Eldorado wheels are unique to the 1968-78 Eldorado and Tornado), and new custom dual exhaust system with twin catalytic converters.
The 1970s era Cadillacs (post 1971) with the rear wheel drive platform would make more versatile tow vehciles as it would be possible to change the differential gearing much more easily. It would be quite possible to have a 500 cubic inch V8 with 4.10 gearing that would handle most of the similar vintage Airstreams.
I have also towed my trailers with a 1965
Dodge Coronet 500 Convertible with the H.O. 383 cubic inch V8 having 335 HP, and 3.90 final drive ratio. The modifications were quite similar to those required by the Cadillac. The one exception was the requirement of a major valve job that included machining hardened seats into the heads to reduce the likelihood of valve recision due to the use of unleaded fuels under the stresses of towing. The car actually does quite well, but I feel safer with the more modern disc/drum brake combinations on my later model vehicles with the twin-cylinder master cylinders for braking.
Good luck with your search for the ideal tow vehicle!