Buzz,
I dont know what length the guns were stocked at, but, these were high grade production guns, typically bought off the rack. In that era, it was very unusual for an adult male to buy a 20 gauge gun. The 20s were likely aimed at a young, female, or, physically small or maybe handicapped clientele.

I do believe it was possible to order these as you wished, but, few did. They went to a good outfitter, and bought a gun.

Best,
Ted