There's an old saying on the NASCAR circuit- - - - -"Horsepower is to brag about- - - -torque wins races!" The same is true for load pulling. Getting the engine into it's favorite torque band and keeping it there as much as possible is the key to moving a heavy load efficiently. That's why the old Detroit diesels needed so many gears- - - -we only had a torque band of 400 RPM to work with (1750-2150) and the bottom half of that was pretty weak. Fortunately, a stovebolt engine has a much wider sweet spot on torque.
The HP rating of a 235 or a 261 is achieved somewhwere north of 3K RPM, and back when these old engines worked for a living, they stayed up there pretty much all day every day. Keep the rod bearing clearance narrow and the oil pressure good, and they will run all day at wide open throttle. I think I'd opt for the OD top gear instead of a close ratio box, and use the full RPM range of the engine, instead of artificially limiting it to low and midrange speed by shifting, instead of letting the engine rev. A 261 with more torque was GM's answer to moving a heavy load more efficiently- - - -and that option is just as good today as it was 70 years ago. The engines I've got on the drawing board with 3/8" extra stroke should do even better.
Jerry
