Plug the vacuum advance on the distributor, and set the base timing at 10 degrees before top dead center .
Start up the engine with the Holly carb on it, and a VACUUM GAUGE connected to BASE VACUUM .
Get the engine down to idle speed (650 RPMs) out of gear, and write down what the vacuum reading is at that speed .
LOOK down into the carb WHILE RUNNING, and see if there is normal fuel flow, any fuel flow showing, or fuel spilling all over the inside of the carb .
Now (if it's still running), put the trans in gear and get a second vacuum reading . IF it stalls, leave it off and look down into carb, note if it's WET or DRY inside and on the throttle plates .
What are your vacuum readings, and at what RPM ?