So many variables...

It sounds like you're building a street car. I would be more concerned about the torque curve than peak numbers. The more low end torque you have on tap, the more friendly a gear ratio you can run for street manners without negatively impacting the fun factor.

Your car has a relatively low curb weight, so a 408 would probably work just fine. Do you have overdrive transmission? A 450HP / 500ft/lbs 408 with a 3.91 gear is a hoot. My dad has that setup in his Diplomat coupe with a 518 transmission. It'll put the car sideways from a 40 MPH role with 275 tires on the back. There is a lot left in the motor too - heads are untouched Eddies.