That extra HP will only be apparent if he's willing to downshift and keep the engine revved up near its upper limit. Lugging up the hills in too high a gear will do more damage to the bearings than letting it wind up and produce the power it needs to get the job done. Depending on whether the engine was originally used with a standard trans or a Powerglide, it was HP rated at either 3700 or 4000 RPM. I'll bet he's not winding it anywhere near that tight. Don't ever let it get below 2000 RPM- - - -that's where the torque peak is.
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!