what goes here
 

I changed the valley pan on my l99 to a ls3 and I can not remember what if anything goes in this threaded hole, its on the back passenger side on the china rail.

Not sure how helpful but I found this pic I took after removing my intake manifold an eternity ago, guessing it's just an unused hole, at least on the L99.

Sorry, I thought it was the vent holes but I believe they're actually on the heads.

I just spent some time trying to find a picture of the engine block from the back side, which I guess is not that common, everyone likes the front pictures, but found this image on this thread (https://www.camaro5.com/forums/showthread.php?t=448785) doesn't look like the hole leads anywhere at least, looks to me like an engine appendix, a leftover from design phase that probably did something at some point. But I'm a geologist by trade not a mechanic.

Just a guess, but maybe it’s a mount for the wire loom

Ok thanks guys I am just going to put a bolt in there to plug it just for piece of mind.

look at the casting . it goes nowhere. could be an extra ground point

And I can't really tell, but it doesn't even look like it is threaded. Just looks like a possible locating hole for something? :noidea: