Only time I've ever spent on a Q-jet's primaries was when I put EGR calibrated carbs on two non-EGR equipped engines. One had a lean surge at cruise, I fixed that and the other I prevented this on, by running one jet size larger.
Short of running an O2 sensor solely to determine if mix is at 14.7:1 or not, not many of us have an exhaust gas analyzer which is pretty much what you need.
Doug Roe's book on the Quadrajet has some info in it about jetting and the power piston IIRC, but it's more work than I've ever wanted to put into a carburetor. There are enough variables in the quadrajet on the primary side that without some way of measuring your differences (and racing only measures WOT) it's pretty hard to tell if you are making a difference or not.
My dad played around pretty extensively with his 454's Q-jet (K20, 6000lbs, fairly wild cam, 465, 205, Gear vendors OD, 4.11's, 32 or 33" tires) to try and wring a few more MPG out of it. He's up to about 11 on the freeway. Knowing how he drives, I think he might be able to wring another MPG or two out of it just by modifying when he shifts, but from what most get out of their big blocks here, he seems to be getting better than average MPG out of it. I know he played around with the jets and rods on the primary side, but he also purchased a power piston spring kit that came with 3 springs, and played with those.
He didn't have anything to determine mix, (O2 sensor, exhaust gas analyzer) so it was just by seeing how the different changes affected driveability/economy.
If you've rebuilt Q-jets before, you know how "easy" it is to tear the air horn off to change the primary pieces, I'd probably wait and see how it does as is before playing around without establishing a baseline.
