Pulling a trailer with the transmission in overdrive is a poor choice, at least with engines like the 216 or 235. Unless you have a very low ratio rear end gear, you'll be below the engine's usable torque range and performance and gas mileage will both suck. That's why there's a cable-controlled manual lockout that prevents the overdrive from engaging with the knob pulled out. The modern-day equivalent would be trying to tow a trailer with one of the small 4-cylinder 5-speed manual transmissions in 5th. gear- - - -the engine speed is too slow to get into the necessary power band for trailer towing. Flat ground running without any extra load is where OD is used. Climbing hills or trailering, not so much! It would be like installing a set of tires a foot taller on the drive wheels. The guys who run the monster mudder tires almost always have to install lower-ratio ring and pinion gears for the same reason.
Jerry

Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!