I've never heard of a 450" 361 combo. What Crank are we talking about? Without knowing anything about the specifics, my first reaction is that it sounds like a an awful short piston, for a street motor. (???) I don't know that I'd feel good about going this route with a #'s correct block (???). A 3.75 stroke should get you into the 420" neighborhood (just off the top of my head), and would still be a reliable street motor.