Here's Oklahoma law on the subject. Notice paragraph (f) states that it is not illegal for restorative purposes if you notify the Oklahoma Tax Commission of your intent to do so...
§47-4-107.
(a) Any person or persons who shall destroy, remove, cover, alter or
deface, or cause to be destroyed, removed, covered, altered or
defaced, the engine number or other distinguishing number of any
vehicle in this state, without first giving notice of such act to the
Oklahoma Tax Commission, upon such form as the Commission may
prescribe, or any person who shall give a wrong description in any
application for the registration of any vehicle in this state for the
purpose of concealing or hiding the identity of such vehicle, shall be
deemed guilty of a felony and upon conviction thereof shall be
punished by imprisonment in the State Penitentiary for a term of not
less than one (1) year nor more than five (5) years.
(b) A person who buys, receives, possesses, sells or disposes of a
vehicle or an engine for a vehicle, knowing that the identification
number of the vehicle or engine has been removed or falsified, shall,
upon conviction, be guilty of a misdemeanor.
(c) A person who buys, receives, possesses, sells or disposes of a
vehicle or an engine for a vehicle, with knowledge that the
identification number of the vehicle or engine has been removed or
falsified and with intent to conceal or misrepresent the identity of
the vehicle or engine, shall, upon conviction, be guilty of a felony.
(d) A person who removes a license plate from a vehicle or affixes to
a vehicle a license plate not authorized by law for use on said
vehicle with intent to conceal or misrepresent the identity of the
vehicle or its owner shall, upon conviction, be guilty of a
misdemeanor.
(e) As used in this section:
1. "Identification number" includes an identifying number, serial
number, engine number or other distinguishing number or mark, placed
on a vehicle or engine by its manufacturer or by authority of the
Oklahoma Tax Commission or in accordance with the laws of another
state or country;
2. "Remove" includes deface, cover and destroy;
3. "Falsify" includes alter and forge.
(f) An identification number may be placed on a vehicle or engine by
its manufacturer in the regular course of business or placed or
restored on a vehicle or engine by authority of the Oklahoma Tax
Commission without violating this section; an identification number so
placed or restored is not falsified.
