Be sure they are set box stock to start with. and you may need at least one tuning kit and maybe some spare parts, like jets or needles. I'll have to go find my notes to be sure, but the 1406's I used ran well enough at base calibration. I fattened them up for drag strip use "one step" rich primary and secondary, per the manual. The shooters that worked were .033s. Remember this is a t-ram setup with lotsa plenum volume. I also ran them 1:1, no progressive linkage. I can do that easier maybe because I run things with locked timing and I don't do low stall converters. YMMV as they say. Your application may like a progressive tip in - you'll just have to try things and see what the combination likes.
Look at it this way - you could drive around with a 600DP, so two 600 CFM Eds are nothing more than maybe a "500DP" running on the smaller primary barrels. The Ed Performers are really mechanical secondary carbs with a weighted air vane to control secondary operation. The weighted air vane secondary won't even come in until you get enough air flow going. (Why I'd like to try the Thunder series - tunable secondary tip in). On my 302 t-ram setup, that was around 5400 RPM. Also don't forget - if that dual 4 intake is a dual plane (I'd imagine it is) then at any particular time the engine only sees half the available carburetion thats passing air.
Here's what "too much carb" on a 300 HP 302 in a 3000 lb 4 door looks like
Get it dial in, then enjoy the "that's too much carb, must not run very good" comments. I got the "haha, nice joke" from the other racers, then ran within 0.1 of my normal ET and won the 2nd race of the year, no more LOLs after that. LOL.
