I'm not especially old, and I vividly remember towing pretty good loads
with 300, 318, 350/51's. Schiddy 70's -90's engines at that.
460 was a big dog, 250 hp (maybe)375 torque.
Heck, look at the Ford 534. A big truck engine. (363hp/490ft/lbs
Not a big engine in a pickup but the engine in a semi.
Grossing 73,280#.
Slow, but they weren't the slowest.
Yep, I think that 6.4 (410hp/429ft/lbs) will occasionally move
15k# ok!