Can a stock crank be turned down to 3.1" ? If not a 383 would need like a 3.22", bigger bore is better but your probably not building a 800-1000+ NA + boost motor, a 4" bore goes pretty far power wise so even a 4.185" probably be good enough but yes 4.28" - 4.40" is even better just wouldn't expect crazy power gains unless using heads that need it.