Kawboy, at GM Institute we used a small book written by Doug, himself, at Doug's Headers about all of the issues with the sonic timing of headers and collectors and primary pipe diameters and length. Kerker used to make tuned pipes for two-stroke engines and all of this stuff came out in several articles in very early Cycle World mags, too. This stuff has always fascinated me, too! Sounds like we are twins of different mothers! Gonna try to find that book you listed.
What puzzled me is just what you alluded to about jets USUALLY needing to be increased with better exhaust flow and all else remaining the same. But, just as Bill said, the headers these guys are using comes with the jets that DynoJet recommends, so I would defer to their experience with their own product. If they are willing to put their name on them, then there must be something else to the story about their pipes to warrant that.
Still, I am not hearing much about watching plug color! In racing (especially drag racing), this is the all-important indicator of just what is gong on with the mixture. I did notice that somebody asked how important it was to run the engine at the desired speed, then pull in the clutch just as you shut off the ignition so as to retain the exact plug color at the desired speed. Well, the big drag teams do exactly this! For our street use, it's not quite that serious, but it does help to do a run down the freeway for a few miles, then pull off and check a couple of easy-to-reach plugs.
Keep in mind that on our sixes, the two outer cylinders are running a bit hotter then the two inner ones since they are farther from the radiator, so they will be lighter in color. I have tested this on my old '83 Voyager when fairly new and it proved to be true. As Kawboy said, stock bikes tend to run a bit rich, and the two center cylinders did run dark brown while the two outer ones looked exactly like I wanted them at a rich tan. At least with NGK plugs a one step hotter plug was too much to correct the center cylinders, so they were just left to run a tad rich. I just mention this so you don't base your color test on the inner cylinders or you could burn the outer pistons.
Now. also keep in mind that I am talking here about the ZN1300 engine with the fuel injection, and there is no (easy) mixture control over them! On your carburreted sixes, you could probably tweak the needles/float levels just right to even out the plug colors.
