273 or 225?
Really depends on what you want to do. If you want the car to be more of a muscle car type, the V8 is nice. If you want a great driver, its hard to beat the slant. I have both in 66 Darts. I like them both. My slant has been built enough to create some nice HP, but not radical. The 273 is stock. To be honest, when I go to cruise nights or shows, the slant gets more attention and comments.
Just depends if you want to cruise or shred tires!!!
Enjoy your car either way!!