Classic/Antique Car Repair: 57 CHEVY 350 ENGINE, chevy 350 engine, vacuum leak

Question
MY CAR HAS BEEN IN STORAGE FOR 15 YEARS AND I HAVE STARTED IT EVERY 6-8 WEEKS.  BUT NOW IT "BACKFIRES" WHEN I GIVE IT GAS?  I CHANGED THE SPARK PLUGS AND THOUGHT THAT WOULD FIX THE PROBLEM, BUT NO.  I AM TRYING TO SELL IT AND WHEN SOMEONE DROVE IT SUNDAY, IT KEPT STALING.  I HAVE A NEW CARBURATOR AND HAVE BEEN MAINTAINING IT REGULARLY.  IT HAS A POINT EGNITION.  WHAT MIGHT BE THE PROBLEM AND DO YOU KNOW ANYONE IN TEMECULA AREA WHO CAN WORK ON THE MECHANICS, IF NECESSARY?  HARRY

Answer
My first thought would be a crack in the distributor cap, but that would primarly backfire but not stall. Check for a vacuum leak and I imagine you'll find your problem. As for as Temecula, I don't even know what country that is in, much less know a mechanic.