Just a few observations. I purchased a 38mm Mikuni from a 78 390 auto(hopefully the jetting was close). I picked up a spigot reed cage and manifold off a 430. The later manifolds are a bit shorter than the stock bing manifold. This worked out because I needed the clearance at the aircleaner end. It is still tight but does fit. On the shorter intake the reeds protrude about 1/8th inch into the barrel. When I bolted it up it was tight cinching down so I took it apart-I needed to grind a little metal off the top and bottom of the barrel intake for reed clearance. I also used the Boyesen reeds that came with the later manifold-bad idea as they were shot. So after wrenching on the thing over and over I think I have it. Jetting was(is) Q-8 needle jet 6DH3 needle 420 main 45 pilot. 2.0 slide ground out a bit. It seems rich but I need to take it somewhere to warm it up for jetting tests. My neighbors allow once or twice up and down the street but I don't want to push it!