Kahuna, if you already have an edelbrock carburetor and do not have a stock carburetor (presumably teapot) it will definitely be best to swap to the dual advance distributor. You will have to have a carb designed for loadomatic to get that distributor to work.
Daniel, thanks for that info! Here's where I reveal that the loadomatic I'm working with is on a 223 six rather than a Y, but I figure the basic info is the same. It's an automatic car and all original, so the loado has only 1 spring and post. The vacuum can is the style that can be disassembled, and it contains a mechanical stop which can be shimmed and a return spring which can also be shimmed. I believe the idea is that the diaphragm movement is controlled by the single spring up to the point of contact with the stop, at which point the return spring comes into play, which gives a 2-stage advance curve like we normally see with the 2-spring setup. I can adjust the rate of early rapid advance with the spring, the extent of it with the stop shims, then the rate of additional advance with the return spring and shims. Maximum total advance is limited by the pin slot in the breaker plate.
So a dual advance distributor may be easier to set up but there isn't one made for the 223, thus the quest for optimization
1954 Crestline Victoria 312 4-bbl, 3-speed overdrive