Re: 258 stalls
Listening around won't find the vacuum leak! Ears are not near sensitive enough unless the leak is huge!
To verify it's a vacuum leak, get it running, hold your hand over the top of the carb choking ot off slowly. If it runs bettrer it's a leak somewhere.
Spray around with a BURNABLE carb cleaner - most don't burn very well if at all. The "green" stuff is based on water - it won't work. Gumout works OK for this -- or use propane like suggested. To test if it's burnable enough, dribble a few drops down the carb's throat, if the R's increase it'll work.
Spray the burnable carb cleaner around carb base, vacuum lines, intake gaskets, booster, trans vac modulator, etc Look for an RPM change just like it did when you dribbled it down the throat.
Check base timing as well.