Re: Model seven
bubb-
The bolt face does not dictate the action. There are 223, 308, 532 bolt face Rem 700 short actions. Swap the bolt out and you have a different capability, the receiver tube has no differences to worry about.
I am 90% sure the 600 action is not the same as the 700 though. As I remember reading a history of the development, the 721 preceded the 700 and was a short lived, albeit excellent, action. The 700 was the design refinement/evolution of the 721.
EDIT: The M-7 has a shorter rear bridge. This means the bolt is shorter, the action and bottom metal are shorter, and the stripped action is lighter. The triggers, recoil lug, and barrel is interchangable (in dimensions) with the 700. The tenon joint on the 700 and the 7's are identical.