I'd personally scrap the stock motor. I don't know about 11's or low 12's, but a built LS/ turbo would be pretty good. Here's a dyno of a stock block LS (well it's got crower turbo cams and a P&P, so I should say stock short block) with 303whp:
http://www.evans-tuning.com/viewtopic.php?t=790
So I'd say if you built the short block and turned up the boost, you could very possibly be in at least high 12's. But it would probably cost you a little under $10K or so (could be considerably less if you find good deals on parts).