The restrictor plate is installed between the carb and the intake runner. This intentionally ruins the signal to the carb, thus requiring richer jetting than an unrestricted engine. So because we have a poor signal we use larger sized jets to compensate.
The reason for the seemingly large sizing in the pilot jet is to provide fuel when the throttle is mashed open and the carb signal/intake runner vacuum goes to zero. Because there is no accelerator pump, no metering rods or other form of enrichment that is vacuum dependent, we're trying to supply fuel till the engine responds and begins making rpm and Bernoulli's magic starts to happen. This is effectively accomplished by a rich pilot circuit.
Once we develop enough rpm to have the main jet come into full play, the ideal situation is to get back to a neither rich nor lean mixture for peak power. Keep in mind that the pilot always supplies fuel, albeit the percentage of fuel supplied to the engine decreases as we build rpm because more and more fuel is supplied by the main. So there is always the balancing act between the pilot and main.
Then there is ignition timing, we'll want an overly advanced ignition timing at low speed to give us a little extra time to burn the rich mixture at idle. Knowing that our flywheel and coil retard timing with rpm, and that we can control that with air gap, we want the appropriate ignition timing to "come in" as we build rpm and begin to arrive at the ideal jetting mixture. Yet another balancing act.
Effectively execute all this and you'll have one ripper of a plate engine.
Can you get good, even great dyno pulls out of what you are suggesting (a pilot in the 20s and a main in the 40s)? Yes you can. But in the real world of the racetrack, you'll get smoked on restarts.
