Be careful. Local law enforcement opinions do not matter even if that opinion comes from the CLEO himself, this is a FEDERAL law which falls under FEDERAL jurisdiction. If an ATF officer saw you, as a regular civilian, with an LEO rifle in your posession, you are up shit creek until the situation is rectified with local LE and your ownership is confirmed as legal.
Contact your local ATF office and get it in writing that it's okay. A standard Post Ban lower receiver costs approx $100, which is NOT worth the trouble you may very well get into since it sounds like you'll just have a neutered Post Ban AR anyway just stamped with "Law Enforcement or Government Use Only".
Oh yeah, one more thing...I just noticed you mentioned that you received twenty 30rd magazines with the deal. If those magazines are marked for LEO use, then I know for a fact that they are illegal for your to own.
Like I mentioned above, just be careful about this. Having all these things and this killer deal wouldn't be worth hard time.