The MSD box reads absolute pressure, not vacuum. So 5 PSI of pressure probably equals 20 inches of vac.
One suggestion is to ditch the pills and put in your own timing curve. Take a look through the stickies at the top of the carb section to get some ideas.
If your timing is right and I assume you have the idle screws properly adjusted, then I would be tempted to try a larger idle air bleed and/or smaller idle feed restrictor. I believe they are both replaceable on the HP carbs. I would get everything else right before messing with the air bleeds though.
I would also suggest a wideband O2 sensor. That will tell you in short order what needs to be tweaked.