Putting a screw in the linkage is sometimes seen as an attempt to make a vacuum-secondary carb into a mechanical-secondary carb, but they don't work very well that way, as that opens the secondaries immediately with no extra fuel, as the secondaries on a vacuum-secondary carb don't have a separate secondary accelerator pump and "shooter" (like "double-pumpers" do), and immediate full opening of the secondaries results in a huge "bog" before the metering system can react and supply extra fuel.
In the same vein, some guys remove the little check ball in the vacuum secondary circuit so the secondaries open faster, with the same result; the check ball is there to "soften" the opening rate of the secondaries to avoid the dreaded "bog". A lot of engineering development has gone into the Holley vacuum-secondary carb, and they work best when they're left alone, although you can "tune" the secondary opening rate by changing the strength of the diaphragm spring - Holley has a kit for that, and they also have a "Quick-Change" kit that replaces the upper half of the diaphragm housing so you can change the spring in about a minute without having to remove the entire housing from the side of the carb.
ALL Holleys used on Corvettes have always had vacuum secondaries, except for the original L-88's, which had an 850 "double-pumper" with no choke, and they were notoriously un-streetable by design.
My original/unrestored '69 Z/28 302 also uses a vacuum-secondary List #4053 800CFM Holley - they all did.