It sounds like you have the makings of a sweet bracket racer.
If you go back to the 600 vac secondary can you see the secondary vacuum motor and associated pulldown link from the driver's seat? If so, make a flag or other device that will show the driver when the secondaries are opening. You may be surprised that they are not open for most of the run. On the RPU when we ran a 4V before switching to a 2 x 2 we modified the pulldown with spring and bleed orifice changes to get it to open early into the run. It still launched off the primaries, which is what I wanted. I also modified the 600 carb in other ways, such as installing changeable air bleeds.
One little caveat here: The things I'm suggesting will make your car CONSISTENT, not necessarily the quickest it can be. I'm all about consistancy and repeatability. I bracket race. The last time I raced the RPU full time was in 1999 - 2000. As I remember I had 9 wins in 12 final round appearances and a track championship before retiring the car to the back of the warehouse; it now gets driven maybe twice a year.
Also, I never flow tested this setup. I did my own cylinder head build. I never measured the compression ratio on this engine. I could be off by a country mile on my setup.
But don't bet on it.
