I have towed my 4500 to 5000 pound Overlander with a couple of different '73
Chryslers. One had a 400, the other a 440. I have no idea what the gear
ratio was, but I do know that neither one came from the factory with a
towing option. Both cars did reasonably well, but we were in the flatlands
of the midwest. If your Lincoln is in top condition I would imagine that it
could handle your trailer.
I just remembered that I have a brochure put out by Airstream that gives the
towing capacities of '77 & '78 cars. They list the Continental with the 460
engine and 3.00 rear axle as having a 6000# capacity. "Cooling and
suspension" options were recommended.
Scott