timing chain jumped a tooth?

[NutmegCT]

I've just returned from my coast to coast drive in my 1960 190b. Car ran flawlessly - *until* I adjusted the points two weeks ago.

Next morning after the points work, car was tough to start. Made metallic klunk sound when the starter was turned. After several tries, engine started and ran smoothly all day.

Next morning, same thing.

I checked spark advance: spark is occurring 30 degrees advance, despite correct alignment of timing chain mark, cam bearing mark, and timing arrow at crankshaft. Prior to resetting the points, spark was occurring at 4 degrees advance (timing chain is slightly stretched).

When I reset the points, I now realize I was turning the engine backwards to move the distributor rotor. I had put the car in 2nd gear, then rolled it backwards to turn the rotor.

Could this have caused the (admittedly old and stretched) chain to slip a gear tooth, despite the chain lock screw being in place?

If so, how should this be corrected?

Slightly rotate and reset the oil pump/distributor gear?

or, lower chain tension and move chain one tooth?

or ... ?

Thanks.
Tom