Pontiac historical services is definately the way to go. My packet just showed up yesterday. For $35 they dig up the original billing history from microfilm for your car and burn a copy. Then they help decode the codes. It even has a 6 digit "engine unit number" that may be the serial number on the block, though my original engine is long gone. If that is the engine serial number, that could be the way to prove "numbers matching", since VIN # weren't on engines back then. You also get a prety good size stack of goodies. For good measure they stuck in a sales brocure for the new GTO's.