Re: 496 Build help
If you're on a smaller budget and you have a worthwhile machine shop locally, see if they have a good 454 block core, preferably a 4-bolt version.
Then get a stroker Scat 9000 series crank (appox $300), some good 6.385" rods and matching forged pistons and take it to your machine shop. Your machine shop should be able to build you a 496 short-block for around $2500-3000 depending on what he charges you for the core.
There are a few other details (such as possible clearancing of the block for the stroker parts) but the rest isn't much different from building any other BB.
But I have to ask, is your car set up for 625 HP? Above 500 HP, you have to upgrade about everything from the radiator to the rear axles, and most everything inbetween.