The air bleed calibration on the stock 2 x 4 Dominators are usually better to start with for a single carb setup. Linkage differences is in the cam underneath to change the opening of the secondaries. Metering block difference is likely in the size of the idle feed restriction only. Unless it's a street car block both PV's, and make sure you have jet extensions and notched floats.
Keep the .028 MAB's, start at .080 on the intermediate bleeds, and try .055 in the idle air bleeds. Jet it for best performance. If you find the car doesn't slow going to larger jets you will need to replace the metering blocks. As long as it does, once the jetting is optimized get a numbered drill set and go .010 up at a time on the intermediates. This will clean up the part throttle richness a 3 circuit carb is notorious for. If the MPH drops doing this go up one jet and it should come back. once you get to .100 and all is well try removing them entirely.
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