You definitely should post a pic of the cowl plate.
123008 is just the build sequence number through the Fremont plant. Since they built Chevelles, Cutlasses, and Pontiacs at that plant, those numbers will all be intermixed amongst the brands.
The build number on mine is 123537, so they were built pretty close together. Mine was built the 2d week of May at Fremont (05B).
Mark