Nick: The 2999 631 part number is the same for all four rear seat belts(two short male belts and two long female(with clasp type buckle NOT push button) in a 70 NON C15 belted E Body car. The 2999 587 part number is for the two front "pull" type belts that are under the front carpet on the left side of the drivers seat and the right side of the passenger seat. They are exactly the same belts used for both C15 and non C15 equipped 70 E Bodies. The date code you mention 1970-2 is indicative of the second quarter of 1970(Spring) and is thus fine for 1970 cars. The correct C15 equipped rear seat belts are all numbered 3508 581 and the part number(as per the parts book) is 4786(they are 1970 only and E Body only, for both hard top and convertible). If your car is a real C15 equipped car, then someone has changed out the seat belts(at least the rear ones) on you. Are the numbers you listed the only ones you can find for the belts in your car? Let me know.