According to Rochester there is a 1/2 inch spacer used under the carb that insures correct vacuum supplied to the carburetor.
Setting the idle for the maximum vacuum will result in a idle where the throttle valve is close (since vacuum is measured below the valve, highest vacuum will occur when the valve is closed). This generally results is a very low (rich) A/F ratio at idle.
When the engine is run at higer RPM's, the A/F mixtures leans out significantly. Then under braking conditions, the throttle linkage with the P/G allows the carburetor basically to go back to idle, and stalls because of the leaned out "run" condition.
Setting the idle mixture control mixture screw at an initial leaner setting AND setting the throttle valve for more initial opening (only a few thousanths) can make a significant difference in the stalling.
Some vehicles use an "anti-stall throttle dashpot" to slow the closing of the throttle valve under braking. I do not know if your vehicle uses such a valve.
As far as the sequence of adjustment:
(1) Dwell
(2) Timing
(3) Carburetor
Jon.
