Personally I think that motor is all wrong for a 4" crank. It will make tons of torque but be out of breath at a low rpm, probably 5000rpms or so. The 4" crank will want a bigger intake, cam and head work. I would stick with the 3.58" stroke, add a bigger cam like a Comp cams 280H or XE274H, a Perf RPM intake and a 750 carb.