4.25 cranks are available for the SB now days and at 4.060 bore gives you 440 cubes. Spark plugs are way easier to change, headers fit better (no need to cut fenders), more efficent heads (better valve position, fast burn chambers, better plug location...) are easily available, rotating parts are way lighter, overall weight is a lot lighter where it matters... SB just makes more sense all around unless you are considering real awesome BB heads like a B1.