If anything slipped, highly unlikely, it would retard everything. If something slipped a tooth (either the cam sprocket, crank sprocket, or distributor gear) I doubt she'd run.
You say she ran fine after the valve adjustment, but wouldn't start after sitting a while.
Back to basics...here's a few things to look for:
moisture in the distributor cap,
carb needs a rebuild,
plug wires are bad,
cap and rotor need r&r,
Do a search here on how to static time your ignition for start-up if you're still having trouble gettin' her to fire. After she's running, you can set the initial timing. But my guess is, you need to inspect and replace some ignition parts and/or inspect and replace some fuel delivery parts...a carb rebuild might be in order.
Let us know what you find and good luck!