If you go with a four barrel carb or 2X2 keep in mind the vacuum advance on the factory distributer will not work properly so you will need to budget in a new distributer. If you run a rochester 4GC carb it will bolt directly to the 4bbl intake without an adapter and depending on the model range from 486 cfm to 600cfm I think. Any way the manifold was designed for this carb. If you can afford the merc crank it would be best to stroke it. The isky max1 is a good street grind camshaft.