That doesn't work with a carb. With EFI, you can raise the fuel pressure to make the injectors squirt more fuel and make up for the greater amount of air being forced into the cylinders (to a point), but it's not quite the same as actually tuning the system for boost. With a carb, you have to do something similar, but it's only because the boost makes it into the fuel bowl and your fuel pressure will actually go down equal to the boost you are running which will starve the carb for fuel. So, you "boost reference" the fuel pump so that for every pound of boost the motor sees, the fuel pump puts out an addition pound of pressure and the carb sees the same pressure it is used to. But adding extra fuel pressure to a carb doesn't do much to add fuel to the mixture under vacuum (at least not until you start pumping gas out the vent tubes), and does absolutely nothing to richen the mixture under boost.
The issue with a 2 bbl is that you really only have one set of jets you an change to adjust the mixture. There is an additional circuit in the power valve that can be used to add fuel when under boost by making it open only while under boost (boost actually pushes it open instead of vacuum holding it closed until vacuum drops below a certain point). The problem is, the PV doesn't have the capacity to go 10 jet sizes (for example). Say the motor needs a 68 jet to run right while under cruise. Runs clean there, and makes for a nice easy driver. But when 12 psi of boost hits, now it needs a 80 jet to be rich enough to keep from melting pistons and detonating since you are pushing close to twice the air into the cylinders. But the PV only gives you the equivalent of a 75 and now you are pulling the head to replace the headgasket that popped, and finding cracked and melted pistons. Or, you run the motor with a 73 jet and the PV brings in the rest under boost, but it's horrible to drive because the kids in the backseat keep throwing up from the fumes and you get 50 miles to a tank of gas. NOTE! Jet numbers are complete made up, FYI.
With a 4bbl, you can tune the primaries for the nice lean cruise you need for a driver, and use the secondaries to bring in the fuel needed when the motor goes from 225 CID to 400 CID. There isn't a way to do that with a 2bbl (that I am aware of).
Besides that, doesn't a 500 cfm 2bbl on a slant make for a doggy unresponsive motor when not in boost? I'd bet it makes for a great race carb where you don't care so much how it runs on the way to the staging lanes or on the return lane, but on the road it just doesn't fit my definition of an UDD.