.620 mechanical Purple Shaft?

All depends... my [email protected] is ok on the street - can putt around at under 2000, just need to get the revs up during
:steering:
But I agree, trying to tune it for best street manners is a moderate PITA.
Again, though, I have 451 inches, not 383. If the OP is sticking to Purple Shafts, the .557 is plenty big enough.