http://www.hotrod.com/articles/hppp-...-engine-build/
Putting a 4 inch stroke crank into a 350 block to make 383 cubic inches, and 460 HP. It isn't the optimum for a race engine, but for a tow vehicle I'm sure it would pull about anything you'd need to pull on an open trailer.
By the time you invest in the 4 inch rotating assembly you might as well build a 421/428 though.
Although I have used a stock bore stroke 350 in my jeep wrecker, if I had a choice like the OP does, I would probably opt for a 389/400 just because the other blocks have the exact same stroke, but a larger bore. In my JEEPS I've had a 350,389,400 and a 455. The 350 did okay but the 389 and the 400 were better towing engines. The 455 was overkill because of all the torque I was breaking transfer cases etc, that just weren't designed for that much torque. I also trashed a stock T400 with the 455. If I hadn't of been so lead footed, the driveline would have lasted longer. The 455 never even knew there was a car hanging on the wrecker sling no matter how heavy it was.