The triangle or the U/C mark on some flywheels is used for doing an "engine stopped" valve adjustment on solid lifter engines. The factory service manual specifies that six valves are adjusted with the indicator aligned with the pointer, then the engine is turned 360 degrees until the mark lines up again and the other six are adjusted. It's much more accurate than chasing a moving rocker arm with a wrench, a screwdriver, and a feeler gauge.
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!