I am assuming you are going to rebuild the shortblock with an over bore? Like the post on the 400 motor and MP cams shows, the more cam you put in it, the faster it will go. The limit is about the 590 cam. The 850 is a good choice for carb. Good machine work, file fit rings, as much compression as you can put in it, and 1 7/8 headers will all help. A solid lifter cam will allow more rpm giving more hp. One key is cylinder head prep. Bowl work and 2.14/ 1.81 valves will do a lot for the build. A good single plane manifold to match a 557 or 590 cam, and if you don't run high elevens something isn't right. This basic recipe put a 383 roadrunner into the low 12.0s at 3850 with a 268 @ .050 hydraulic 540 lift cam (stock stamped rockers!)that quit at 5600/6000 rpm due to valve float issues. You would have more cubes and a better cam if you go 557 or 590, and the ability to ring more hp out of it with more rpm.