Does that cable shifter happen to be spring-loaded so there can be a "pre-select" of the rear end shift and then a quick unloading of the drivetrain by pushing the clutch pedal or backing off the throttle when shifting the rear axle? A trucking company in California where I ran the maintenance shop had an old frame with that type of manual-shifted rear axle.

A 261 engine would be almost a bolt-in fit if you're looking for more power, but anything newer will require some major fabrication. I'd suggest a 292 and a SM-420 transmission, if you think the rear axle will stand up to the added torque and horsepower without needing a trip to a dentist to get the gear teeth patched up!
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!
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