To check for slop in the chain, rock the crank back and forth by hand. You can feel the added resistance when the cam starts turning (or you can watch the distributor rotor for movement.) Take it in one direction until you feel the cam start to move, then back it up until again you feel the cam start to move. More than a few degrees (5-10?) and the chain is loose and should be replaced.
Have you tried "power timing" it? Advance the dist a bit at a time, until it pings on hard acceleration. Back it off a hair and you're done. Primative but effective.
