Far from my area of nominal WW2 material culture “expertise”, but in my travels I have come to associate Machine Gun Canvas Covers C-67701 (Cover, Breech) and C-67703 (Cover, Muzzle) with the later Browning .50 Caliber Machine Gun M2 , and as items for the spare barrel: https://www.bmgparts.com/products/m2barrelcvr.jpg