In the early 1960s we pulled a 4000 pound TT 6000 miles with a 1960 Country Squire about the same weight empty, carrying at least 1000 pounds of people and stuff, 352 CID FE block and CruiseOMatic. The combo could keep up with traffic, cross the Rockies in Montana on pre-Interstate roads. But we did wear out that car (transmission, u-joints, rear axle, wheel bearings) in less than three years. We replaced it with a 63 Colony Park with the 390 CID version of the same engine, same transmission, wore that one out in three years.
We had friends who towed similar sizeTTs with full size sedans, using the big 3.8-4.2 liter sixes of the day or 260-300 inch V8s and three speed manual or two spead automatic transmissions (FordOMatic or PowerGlide). They just towed slower and didn't pass anybody. They replaced the cars every 2-3 years, as the rusted out that soon anyway in Michigan.
Times were different, in that we did not have Interstates for most of our trips, we cruised 50-60 mph most of the time rather than 70-80, and the big trucks ran even slower. Compared to today's equipment, tires and chassis parts were not as well made with respect to materials, but compensated some with larger sizes.
Considering how quickly we wore out those cars, I would not use a 50s classic for any serious amount of towing, a tow vehicle of that vintage has to be treated as disposable. Upgrading engine and transmission with modern components would be a start, but really you need to upgrade all of the chassis components, with particular attention to suspension, steering, and brakes, for safety towing at today's highway speeds and for longevity. I remember when car mags started doing comprehensive road tests in the early 60s, to learn that many cars of the era, and most earlier cars, when fully loaded could not achieve a panic stop from 70 mph with showing brake fade; front discs or big finned drums were soon to follow.
Think about how you plan to use this. As a show combination, drive carefully to get to shows, it is probably OK. For extensive use as a towing combination, I would be thinking about police interceptor or maybe even Grand National class of chassis upgrades, if you can still find any of those components. Otherwise, you could be grafting on late 60s or early 70s components (much later and you run into the unibody problem). Then the car is no longer a classic, rather a custom.
Tom Test
Itasca Spirit 29B