Most, but no all, 1st Model 1920s came with the tail block (bolt shroud) drilled, tapped, and plugged from Utica for the Lyman #54 peep sight. The Mabel's S20 is the alternate peep sight, but you will need to d&t 2 holes in the left side of the receiver, straddling the ejector, for it. The 2nd Model 1920, 20/26, came from Utica with a Lyman #54 mounted.
You might try Gary Fellers in TX. There is a guy in Omaha who might have what you're looking for. I'll call him tomorrow and ask him.
Jeff
