Bingo, Dave. High gear worked along with a cheater pipe.
What's the sign of a bad harmonic balancer? The pulley and balancer itself are solid as a rock. No separation, wobble, etc.
Later, I'll start it up for a few seconds making sure I get to the 1300 RPM and more to see if the sound is still there. There's no water or radiator but that should be OK, right?
1948 3/4-Ton 5-Window Flatbed Chevrolet 34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.