I voted 6.4 but it was tough. Would you be stroking the 6.4 or just run it as a takeout? Keeping VVT? 6.4 is a great engine, awesome flowing heads and a stout block, BUT, a 400 stroker (4.25" arm) would be a very nice street package. Sure, the Apaches flow 330-340 ish stock, but you have to twist 392" pretty hard to take full advantage of it. A 500" BB with some street type heads (trickflows, edelbrocks, etc) would make a mountain of torque which is nice for a street car.