That's the way it should be! Build the car for YOU. It's what I did. Not original but what I wanted. And the 413 is a monster engine. Same stroke,smaller bore than the 426. Have it tested then bored out .060. Maybe not exactly a 426.. more like 425.5 but who cares. Obviously some do. Runs great with horrible gas mileage but that's how it was and is. if you know what you want a 413 motorhome engine is just fine.