Here is the firewall after media blasting. The wax crayon markings are clearly visible on the bottom photo. The dealer used a hole saw to cut the opening for the plenum. Laying on the top of the firewall between the 2nd and 3rd hole is one of the cut-outs which was laying in the fresh air vent inside the car when I removed the kick panel. 

Not really sure what the numbers mean. I originally thought it was related to the model 12637, but I wouldn't think that would be necessary. If I look hard enough it says "penske test car"