SlantSixDan gave you a link to some good sources for DITY work.
Just for grins, is the exhaust manifold heat riser working properly? The fuel mixture needs some heat to remain a vapor. If the heat riser isn't working, it's taking longer for the engine to warm up which can impact fuel economy.
While on the grins line, are you enjoying the extra power from the 2 bbl? If your driving style has changed as a result, expect lower fuel mileage.