You would need a broadcast sheet or original window sticker to know what came on the car.
That said, for 1970 Challengers;
M83 - Rear bumper guards - Standard. ( These are the plain chrome style)
M85 - Bumper guards - Front and rear rubber inserts.
M85 was available on all 1970 Challenger models, the cost was $23.80
T/Ake care,
Barry