The method of setting float levels where you turn the mixture screws 10 turns down, remove the domes, and set the fuel level so it is even with the top of the nozzle tops has been written about many times on many sites. The site / article where I was first introduced to the method is at the link below.
https://zcarguide.com/tuning-adjusting-datsun-240z-su-carburetors/
I learned a lot from the article but 4 key things in particular.
First, adjusting SU carbs really hinges on getting the floats set right first. If you don't have that right, then I find that everything else ends up being a compromise. BTW, some disagree that setting the floats is super important but I am a believer and kool-aid drinker on the theory. If you don't get the fuel level set right in the floats then you end up setting the mixture level significantly different than 2.5 (plus or minus .5). When you do this you end up shifting the needle zones up or down and outside of the intended range in the power band. Worse, if the float adjustment is off by enough, you can't even get the mixture adjustment screw to cause any change. Again, this is all my opinion...and is shared by some and disagreed with by others...which is fine. You will figure out what works for you.
Second, the 10 turn down method was the only method that, for me, was exact and repeatable. I just could never get the .55 hanging down while sucking (no comments Site) or clear tube set to 23mm or whatever to work for me. No doubt, it works for some. To me though all of the other methods, at the end of the day, are trying to get the fuel to a certain level in the nozzle (10 turns down), so why not measure using the goal?
Third, once you have the floats set, using a Color Tune to set the mixture works really well for me. A couple of Color Tune tips though. 1) use the Color Tune in the dark...or low light. This will let you see the colors better. 2) Clean the Color Tune often. Once the engine has been running with the Color Tune for 1 minute or so, I find that I cease to be able to see the distinctions between Red (rich), Blue (ideal), and White (lean). So, I pull the Color Tune plug and clean with carb cleaner spray often. It is a kind of tedious process but it is accurate and repeatable.
Fourth, I use the Color Tune at two rpm levels- Idle and about 3k rpms. I let idle run a little rich (red)...which makes 3k end up being about right (blue).
Also worth checking if you are having fuel delivery issues is the little flexible hoses that connect the float bowls and the nozzles. Make sure you use ZTherapy or similar hoses that are super flexible. And, make sure the hose is not creased...impeding flow.
I assume that your nozzles are moving up and down correctly and closing fully when choke is off and opening when choke is on.
Stay with it. You will figure it out.
EDIT:
One more thing...and many may disagree with this too. I have never had any success getting the 3 screw carbs where one float bowl lid has longer ears and you use a longer needle jet to work. This arrangement causes the float to remain angled lower in the float bowl, which I think causes it to get hung against the float bowl wall. So, if you have a carb set where one has the lid with long ears and longer needle jet, and you can't get the float level set exactly and reliably, consider locating another short ear float lid. You can use any short ear float lid from any round top carbs. I had an extra set of 3 screw carbs sitting around and scavenged the short ear lid from that set of carbs.