273 Commando or not?

I have always "relied" on the fender tag for the information pertaining to my 66 Barracuda. Last night I was looking over the insurance re-newal, and noticed an error in the VIN number. As I was verifying the VIN I noticed there was a "D" in the VIN which translates to a "basic" 273 rather than an "E"which would translate to the 273 Commando. When I bought the car I checked it out and it does have the correct rear end, the correct leaf springs, the front disc brakes, and all of the "external components" associated with a Formula "S" 273 Commando car (dual point distributor, four barrel intake/carb, valve covers, air cleaner, even has an original "Blue Streak" spare in the trunk, etc.), but now I'm wondering if the engine is a TRUE 273 Commando.....What would be the easiest steps to take to verify that the motor is a real Commando, 10.5:1 235 horse motor? (I don't have a build sheet either)
There are several things I was planning on doing to it, but if it isn't a Commando engine, I'm not going to waste my money.

(This probably explains why the fender tag says the car came from the factory with GOLD paint, but when my buddy painted it he said he could find NO TRACES of gold paint on the car anywhere......Can you say WRONG FENDER TAG?)