An inline 6 was designed to pull, and the only problem with using one for trailer towing is the lack of one big enough to pull with the big V-8's without sacrificing road speed. I can out-pull just about any automotive engine with my 4-cylinder, 58-HP Perkins Diesel tractor engine, but it's got a maximum road speed of about 12 MPH!

The 300 cubic inch Ford 6-cylinder is about the biggest inline 6 that's been made recently, and it's been out of production for several years. If some manufacturer wanted to design a 500 cubic inch gasoline I-6 with sequential direct fuel injection and a dedicated towing package to go with it, I'm sure the V-8's couldn't touch it for pulling power- - - -not so sure about fuel economy!
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!