Ditch the opti and do a 24x LS1 pcm swap to take care of the high rpm ignition issues, get a good set of rods and pistons as well. Have Loyd Elliot or Advanced Induction port the heads and spec a camshaft.

Both guys are well known in the LTX community and if you need more info, head over to the LT1/LT4 section of LS1Tech. I think someone already had the idea of destroking an LTX a few years back.