In 1937, Savage Arms Corp. introduced three new hammerless break-action guns -- Model 220 single barrel, Model 420 over/under (and the nicer stocked Model 430) and a side-by-side with a trigger-plate action the Model 320 --
Savage Arms Corp. must have decided competing with their A.H. Fox line wasn't a good idea and teh Model 320 was gone by the 1939 catalog. So, to get a lower priced double they added the Fox Model B to their offerings with an insert included in some of their 1939 A.H. Fox catalogs.
Savage took the internal parts of their J. Stevens Arms Co. No. 530 and put them in a slightly nicer profiled, black gun metal finished frame with a bit nicer stock and called it the Fox Model B. The Model B was included in their 1940 A.H. Fox catalog --