Its kind of complicated and relies on a tag on the left side of the engine block. Hopefully you can get to the link, its the pages for determining the main bearing clearances from the service manual. Says its for a 4.4L but its the same for a 4.2L.
http://home.townisp.com/~markcanning/camaro/4.4L main bearing journal clearance.pdf
http://home.townisp.com/~markcanning/camaro/4.4L main bearing journal clearance.pdf
