I rebuilt a 6139S for my '73 340, and I have had to re-work it due to the aggressive cam. It was running lean, I have since added #1966 metering rods and a lighter tree spring. Thanks to Demonsizzler (on this site) it is almost there, (it need jets now) but I wish I had done better homework beforehand. Live and learn. But was it worth it? Yes! It is easily the scariest engine I have rebuilt, it just runs and sounds so nasty, and the TQ is extremely responsive. Ask Demonsizzler his advice on which of the above carbs to use.