Looks like a solid project. Any idea why the package tray has an overlay of sheet metal ?
Since you mention the CRG report, have you checked for the firewall piercing for the Muncie speedo cable that would be present on an SS ? That would be another indicator of this being an actual L30 car. The build date of the Muncie is curious also. It is in line with the build date of the car, but the L30 never received a Muncie trans, they were all Saginaw. Use a mirror and light to see if there is a partial vin stamped on the top of the trans. Which, if that is a match, why the 10 bolt rear with a close build date ? Very interesting car...
I have an 02C built at LOS with many of the same options but an automatic, which, thankfully, eliminates all this guesswork.