I don't have a ton of LS experience, but it seems like a lot of them have oiling issues to the rod bearings. Last one I built was a 402 cubic inch road race engine for a guy. The core he brought me was an LS2 core and it had 2 spun rod bearings.
Crank probably needs to be reground, rods need to be replaced. Throw some new bearings in it, a good
oil pump and pickup, and let her roll.