[George Snyder]

All very good advise posted!

I do have a question for you though.

Have you removed the carburator off the engine? If so did you install a new carb gasket? If the answer is yes & no then my guess is that the vacuum advace is getting manifold vacuum not ported vacuum from a poor seal on the carb to manifold.

A GM stock Hei units usually only produces 15-18 degrees of advance. Your case 18 +10 equals 28. I am guessing that with weights & springs only, your distributor may be maxed out at the 3k you stated. The stock vacuum advance unit usually will add 24 more degrees.

A SBC under light throttle cruise performs best at 52 degrees of total timing.

If you need to replace that distributor, may I suggest you try a MSD Pro Alumn Billet HEI. Really nice unit!
Good luck ,
Bud