I have 2 real D/Darts. One has a modified 273 race engine with some unknown fenderwell headers. The other has a 380 hp 360 Mopar Magnum crate engine with Doug's D450 headers. Supposedly, the crate engines were putting out around 405 hp so it would be around your build. With that much hp, I would go with the Doug's. They are pretty easy to install. I did have to shim the motor mounts up a little bit. There are a could videos on YouTube of me backing them out of my garage. Look under 1966 LO23.