Time to rebuild?
I have a few things to note;
1) Is the choke thermostat the same unit between Holley 1920 & Carter BBS?
2) Is the new base gasket exactly the same thickness as the OE?
3) If the answer to either of the above is no, the choke calibration will be wrong.
4) When the choke is closed, the pull off(break) dictates the initial start-up idle & drive off quality. The timing of the choke opening beyond that is dependent on the thermo coil.
5) If the carb is raised or lowered, You have altered the timing/calibration, same if a different model engages the rod at a different level.
6) I had to make a gasket for My 3.9 Dak 'cause the kit didn't include the extra for the spacer, it was thicker, & pulls the choke open too soon. I have a sag during the warm up
cycle between cold start & roughly 80% fully warm.