Marlin.  The tube between the scope & the front mount was necessary because Marlin scopes had neither the groove used on A5s to prevent rotation within the mounts, or the ribs of Lymans & other makes; a crude means of preventing rotation, but evidently cheaper than attaching a rib.

Odd story of how Marlin got into the scope business is related in Brophy's Marlin book.  Started out with request by Sears to manufacture scope mounts for them; Marlin improved & patented Sears' idea, & produced mounts for both, the scopes for both being manufactured by Wollensack.  Marlin's scopes were called No. 1 & No. 2 Models, but mounts were the same, without a separate name.  Wollensack terminated commercial scope production during WW II, & didn't revive it after the war.  Don't know if Marlin continued to offer scopes post-war--by then, it was a very crowded market.