Need help picking power plant.

Had a '69 Dart with a 3.23 rear behind a 440/auto and it didn't have any problems showing the tail lights to most anything on the road. If 500 horses is your goal, you really don't need to go bigger than a 383. That power level would be a handful on the street though. I would choose the 451 stroker because it would be a little more street friendly. I would stick with a low deck B engine for fenderwell, header, and firewall clearance. Durability would not be an issue. You really haven't lived until you've nailed the throttle on a big block A body.