also, pistons will be about 450g and will use a roller cam in the .700 lift range. i'm thinking the shorter stroke will eliminate some side loading and with a longer rod for better rod/stroke ratio may produce better power and help the block last longer than a 4.000" stroke.
the 4.125 stroke should make better torque which I need as my best 60' with 408 has been a 1.45. but with a 6.250 rod would give close to same r/s ratio as my current 408 with a 6.123 rod.