Do you have THE RIFLEMAN'S RIFLE book ?
OOP and will cost you, but it's THE reference on 70s.
Might have been back to the factory for work, or may be a gun built from parts.
The value of some 70s got so nuts that fakes abound.
Detailed pics would help the folks here who really know 70s help you.
Detailed means high quality, well lighted and a lot of them.
Last issue of Rifleman had an article by Senich that pretty well put the "military model 70" myths to bed.
Good luck.
