I did the same upgrade on a 1983 Magnum II. I forget which way is which but when you adjust the mixture screw (with a 5/16 inch nut driver) when the ped is running......if rpm goes up your are going lean. The other way will be rich. If I were you I would also "modify the intake port on the bottom of the manifold a little to match the square port on the cylinder.
Another tip: Go rich on the mix, especially if your air filter is pointing toward the front tire. At high speeds too much air will be forced into the carb and the engine will bog.
Do a "search" for "Things not explained" in this forum. I had alot of fun doing this upgrade.