Andy, that's what I've figured out with research. I was thinking maybe being 577 cubic inch it may be a larger engine,but,it's all internal stroking that makes the 429 a 577. I feel it's a very cool car as well! I'm drawn to the car by itself,then there's the facts of it was driven by Ronnie Sox and won the championship that season,was powered by the cat in the hat Jack Roush and owned by Dean Thompson! It's a piece of history.
Cheers,Adam