ASA has been using a modified version of the LS1 for a couple of years. Next year's move up to the '6 is merely an upgrade.
The neat thing the ASA guys also have is an open-loop, user-programmable, engine controler and the ASA camshaft which, while having only .525 lift, has a ton more duration. But---don't get any ideas if you got cats. The ASA cams needs open exhaust to gain any power over the 02, LS6 production cam.