I have the run on issue as well, my 292 is quite stock but no blowy,good comp.i kept blaming the ign. switch. after reading these posts I followed the advice ted had given. retarded the timing a bit,got idel to 550 no run on,canadian gas which is terrible with all the additives. seems betters also had a flat spot   when upshifting and engine cold. (manual 4spd with od in 4). I also hooked up the exhaust flapper to get a bit more heat to the intake. still have to go for a good  run but appears to be much better intake with  Holley 600cfm 4ve.

just filled up with mid grade gas. no more run after sign off