When going to 2 carbs, the main system is running on airflow through the venturiis and so should be reasonably close to right whenever venturis are excited, but the accel pumps put out a fixed anount of gas, so you have twice the gas going into less manifold area and an overrich condition on acceleration. He advocated drilling a bypass hole through the check valve (the beasty in the center plug of the Stromberg), starting at about the size of the discharge so output was cut about 50% and the surplus dumped back into the bowl. Others drilled right through the floor of the bowl into a passage there. Barney's method gives you a cheap and easily replaced part to play with. I suspect the off-idle circuit may need attention too, as it is not really calibrated to airflow in any way, and you now have two of everything. This circuit is controlled by the idle jet. Idle circuit gets its fuel there too, but it has its flow customized by adjusting the idle screws. The Ford service bulletins give a road speed for when the venturis come into play with stock setup, and it's pretty high--it would be higher with two carbs.
Thats a very simple and cheap way of cutting back the amount of fuel. I've basically done the same but with smaller power valves. You can get any size you want now from people like the new Stromberg 97 company and Vintage Speed. I always wondered how they done the same thing back in the day as I've never seen any evidence of power valves being available in different sizes.
The Jalopy Journal
