I am running a 700R4 (.70 OD) behind a built 250 with 3.50 9"Ford in a 41 plymouth 2 dr sedan with 215R75 x15 tires and it will tow my T roadster at highway speeds just fine. I would think that you will be just fine. When I first built the car I had a 3.08 gear and even with no trailer every time a came to a slight grade it shifted out of OD would run fifty feet then shift back to OD then do it all over again untill the road flatened out. We took one trip with the constant shifting and decided that the 3.08 had to go. installed the 3.50 gear and increased the gas mileage from 13/14 to 18/21. Got 20 mpg and better last year coming home from convention towing the roadster, interstate running 55/60mph on cruise control most of the time.
