It's virtually impossible for a stovebolt cam gear to jump a tooth without destroying the gear and stalling the engine due to the cam not turning at all. The slipped timing gear hub is a definite, though very rare possibility.

Here's a quick check- - - - -watch the valve rocker arms on the #6 cylinder, the last two back by the firewall. As the exhaust valve (last one in line) stops moving and the intake (next to last) begins to move, the pistons on both #1 and #6 should be at the very top of their stroke. You can monitor piston movement with a piece of soft copper wire through the spark plug hole (definitely NOT a screwdriver!) as the engine is turned with the fan blade or a pry bar through the starter hole engaged into the flywheel teeth.
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!