I can tell you how one of my 421 Cubs was set up. 0.045" squish, 185 psi (20 cc domes), dumps drilled to 0.125", 60 pilots, egn needles. I also ran a different set of carbs that were drilled to 0.120" with some different needles (don't remember what they are.) Its funny that one my stock chassis, the 0.125" dumps worked fine, but when I went to a 50 lb lighter chassis - I had to turn the pjs all the way in and still no heat on the plugs.
Another 421: 0.052" squish, 170 psi; 38 mm a/s PWKs, 0.118" dumps/mains.
Another 421: 0.050" squish, 180 psi, 39 PWKs listed above.
All 3 of these motors run about the same, even set up that different. I'm convinced that you can setup a 421 any way you want, and it'll perform pretty good. All of these run 4.0s with an average rider and 3.8s to 3.9s with a jockey. It's in the fine tuning/perfect setup that you get it to really fly (e.g. 3.7s).