I think fitting Pratt and Whitney R3350 cylinders and pistons is a better way to go. They give you fractionally over 3 litres per cylinder. Someone has fitted large radial aero engine cylinders to a pre-war JAP engine (in a GN?). That must have a far more fragile bottom end than the S&S? The bevel drive and drive belt might need beefing up a bit :-)
Wilson
