sean hyland and dss prep their blocks to the extreme. but they also cost the most. if you are wanting between 450-550rwhp then get one from vt. vt is the most resonablypriced and they hold a lot of power.
www.vtengines.com is what Im getting built up right now by Murillo motorsports. My Cobra sportsman shortblock with all the gaskets and labor and getting my heads milled and everything out the door including tax and labor is 6Gs. Not bad considering I'm having a 6 time National Outlaw champion build my Cobra motor. If you are reasonably close to Texas I'd get him to tune it. I hear he's real good and so far hes been real nice and straight forward with me. No shady business whatsoever, just very down to earth, and very reasonable.
Someone just turned me on to these guys. Best prices on engine kit's I've seen yet. If you want to put it together yourself that is.... http://www.modularperformance.com/catalog.asp