69 Impala 427 - Could it be a CoPo?

[69LM1]

Question. I just picked up a 69 2 door impala 427/390, 3rd owner. It is all numbers matching, down to the rims, although unrestored. It has always lived in that area. It was not sold as anything special, but the owner stated that when he bought the car from the 2nd owner, that owner claimed that he bought it from a local government auction and that it was originally ordered for a local police offical, along with a batch of 4 door police cars. As Florida does not keep any paperwork past 12 years, it is hard to prove and thus only a story at this point. The claim is that the rear end, a 12 bolt with 3:31 posi from the factory (along with the 427) could only be ordered via the CoPo system. Does anyone know if this is true or not, and if there are any other ways to tell?
Thanks,
Rich