Thanks gentlemen. Only thing I did was to reset the points to 0.018" (4.5mm).

But to turn the rotor, I put the car in 2nd gear - and stupidly pushed the car backwards. Thus the engine was turned backwards. That's why I'm thinking the chain jumped a tooth on the distributor (idler) sprocket.

Crankshaft damper shows static timing is at TDC; cam mark and chain mark are aligned. Dist. rotor points to the mark on the dist base.

But crank the engine and strobe shows the spark firing at 30 advance.

I'm no mechanic - but if damper, cam, chain, and rotor are correct, then the only thing left to adjust is the chain.

(right?)

Edit: breaker plate isn't binding; vacuum advance works correctly. Rotor snaps back into position when twisted by hand.
Thanks.
Tom