In addition to the DUCK/MAGNUM Model 21s, the Model 21 Trap Grade (in the 1930s) except for the Model 21 Trap Grade Skeet Gun and the Model 21 Trap Gun from 1940 onward were "standard" with a recoil pad.

Now to the gun in question. Look at the grip area!! Either that is a pistol grip stock that has been straightened or it is a restock.