Upon further investigation this morning the stalling on return to idle symptom can be replicated any time the throttle is held open,for more than a few seconds ( about 2000 RPM )and the let close on it's own. The return to idle is gradual until about 1200 hundred RPM or so and then drops right off into the stall condition. Even if you try to bring it back as it begins to falter it seems to have a hard time responding. This engine has not been driven for a while but has been tuned and has fresh fuel and other than blowing a bit of smoke it appears to be in good overall shape.
I also have the common " run on or dieseling problem" and would be interested in any comments with regard to solutions for this? As well I would ask is it OK to put the automatics in gear to stop them as per the stick shift cars. The carbs are the SU-HIF6 version with the overrev valves in the throttle plates as per Canadian specs. Thanks

Just for grins, try unhooking the vaccum line to the distributor.