"Drive it like you stole it"- - - - -these old engines are a lot tougher than the snowflakes with lace on their drawers think they are. The cylinder head design won't allow much over-revving unless maybe you're running wide open in granny gear on a SM-420. Any cruising speed under 4K RPM in high gear isn't likely to do much damage to an engine with a good lower end, particularly one with good oil pressure and rod bearing clearance under .002"
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!