Chris,
This probably should have been obvious, but I just thought of something. If that chinese carb is designed to work with the Earthquake, which is a non strato clone of the GZ4000/Ryobi 10532, then I wonder how the carb would work on a Ryobi if you didn't connect it to activate the strato valve? You would essentially be turning the Ryobi back into a GZ3800 non strato saw. Might be really easy, solve the question about differing venturi sizes and fix the carb problem. I might just try it.
Look at the MCulloch XM40 saws, or the Partner 350S - these are copies of the Zenoah G3200 chassis, but use the 35 or 40cc strato cylinders with the strato ports blocked off. They put a 28/64" carb on it feeding the conventional intake. I never ran one, but they have to be at a serious disadvantage giving up all the strato intake port area.
Keep in mind that performance is about increasing the air volume - there is never any problem getting enough fuel in, as even a tiny carb to flow enough air for all the fuel you could possibly need.
I have been re-thinking the carb size on these and I doubt going from 24/64" to 28/64" would be a problem. My 40cc 142 came stock with a 34/64" carb and while it runs great it does not turn the rpms I'm getting out of the GZ4000-based saws, but the large carb still meters fuel just fine. So I expect the slightly larger carb would be OK.
This weekend I should get a chance to try out my ported GZ4000 clone with the modified air valve - if it can pull the rpms the Ryobi does then I won't put the bigger carb on. If it can't I will either get a real Zenoah air valve or look at the larger carb - but if I go with the larger carb I may go back in and increase the conventional intake duration to take better advantage of it.