By 1927 J. Stevens Arms Co. introduced their more streamlined No. 620 pump gun, and reduced their old J.M. Browning designed No. 520 pump to being marketted under their lower priced Riverside Arms Co. name. From the 1927 J. Stevens Arms Co. catalogue No. 57 --
By 1930 Stevens changed from Riverside Arms Co. to Springfield Arms Co. for their lower priced line, and the No. 520 was no longer catalogued.
If you just got it in an arms length transaction, you know what it is worth. From what I see they languish in pawn shops at $175 and the Cutts would make it worth even less.