This is OK.
Now try 15 degrees initial.
The rpm in neutral should drop slightly.
Then try opening the primary mix screws.
The mixture should richen; and the rpm and vacuum drop when shifting into drive should be the same or less.

If it the rpm and vac drop going into Drive doesn't get better, then maybe this will be about as good as it gets with this carb and engine (at least without modifying the carb).

Qs Before going deeper, what do you mean by "mixture screws don't react as they should"?
If the secondary mix or primary mix screws are closed, does the engine die?
How about if they are all closed?

The primary transfer slots showing a little less than square may be OK. QF slots may be wider and/or longer than a classic Holley. This may or may not cause problems. So lets find out.
First -
Test. While the engine is idling, close off two and then all four of the Idle Air Bleeds (IAB) with your fingers. If the RPM goes up, then the engine likely wants a richer mixture at idle.

If it wants richer, then I think its worth the effort to give it what it wants. It may take a few iterations of testing. My inclination would be to try smaller primary IABs right at this point. Wires in the IABs will work as an expediant if you dont have smaller ones on hand or just want to test quick. (Run the wire under the aircleaner gasket so they can't fall into throttles.)

If it did not want a richer mix at idle, then retest at 17 to 18 deg advanced including adjusting idle mixes. Go with which ever timing setup seems to run better in Drive.

Second -
Having established the idle, the next thing to test is the off-idle. Off-idle fueling is also idle circuit except the idle ports contribute a small fraction of the fuel as more of the transfer slots under the throttle get exposed.
Test a.
Drive it. See if there is any hesitation or lazy response under normal acceleration situations on local roads.
(All tests should be without secondaries; disconnect the link if neccessary.)
If there is hesitation or lazy response, then the primary throttle position will need to be adjusted. If not, then a little less than square is probably OK.

Test b.
In neutral, very slowly open the throttle so there minimal accelerator pump shot contribution. RPM should go up with no flat spots. Some people have better luck/skill with this test than others. Urich recommends doing this with a sensitive tach. I do it be turning in the throttle screw so it is super slow.
If there is a flat spot, then the idle circuit needs more fuel. Try a slightly larger pair of Idle feed restrictions.

If it seems like its working, do the same test driving. Very slowly open the throttle from idle. If there is a flat spot, same deal, it needs more fuel in the transition. In this case, either slightly larger fuel restrictions or slightly smaller idle air bleeds.