heres a fast way to set the timeing with just a vac gauge on a full vac port off the carb...

hook up the vac gauge to the carb port for full vac at idle.

advanc the dist/timeing till you get your highest vac reading.

then back it down one #( example..high is 19,back down to 18) then snug the clamp on the dist so it wont move.

test drive it,that will get you in the ball park.

if it still does the clatter..then test it with dist vac pluged like posted above.

when you have a light on it,note where the timeing mark lines up on the timeing tab for later referance.

if its a aftermarket cam it may want more advance,so it may go past the #s on the tab..so you estamate it a little.

one thing I have learned..what is said to be done does not allways mean it got done correctly