I have built dozens of race engines over the past 40-something years, and every one got a 20 minute run-in immediately after startup. If the bearing clearance and oil pressure is good, the speed doesn't cause any problems at all. Just have everything like ignition timing, coolant, etc. as close as possible to correct before you fire the engine. Tinkering with carb adjustments and timing to keep the engine running and letting it idle on initial startup will wipe out a cam in a hurry. Sorry you had to learn this lesson the hard way!
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!