Yes, the only mod necessary is flattening the pinch weld.....and that's with the big block 727 case. I believe the small block 727 case fits a little better. That said, like
@toolmanmike said, the 904 can be built to handle plenty of power with parts available today. They have no trouble handling up to and beyond 500hp. Bucky Hess ran a 904 in his SS Hemi Barracuda for years. He got deep in the 9s with it, so they definitely will hold up. I'd leave it the 904.
