6.1 or 6.4?

I picked up a 6.4 off market place and it was cheaper. all in 2800 shipped to my house. I have already purchased car motor pistons and a bigger cam. looking for 500hp out of the box. we shall see. going in a 2900 pound 72 demon.
my dart sport is a handful already with the warmed up 5.7 so this one should be a hoot to drive!!