[blykins]

425hp isn't much for a high revving SBF. I'd go with a big bore, short stroke combo, like you say, maybe a 331/347. I wouldn't trust a factory block for very long turning 7500-8000 making over 400hp. I would go with an aftermarket block if you plan on staying at WOT for periods of time.

Of course making that kind of power at that high of rpm would basically mean that the engine would be somewhat turdish on the street.

However, to get there on sort of a budget, I'd go with a set of AFR 205/225cc heads, a large solid roller camshaft, and a large single plane intake, like a Super Victor. As the others are saying, you're gonna need to spend a lot of money in the valvetrain area. Light valves, titanium retainers, locks, stud girdle, etc.

With that combination, you'll overshoot your 425hp goal by quite a bit....another reason to not use a stock block.