With the factory magnum cam and springs there will be little to no gain changing intakes from the beer barrel to really anything. It’s a pretty good match for what the magnums were designed to do. Now, if you upgrade the cam and springs there is lots to be had.
I have a 209 duration cam I'm going to put in it agree on the factory cam, although it works well in 4 low, and surprisingly up to 60 mph if you floor it and keep your foot in it