As far as I know the retaining screw was always above the center of the breech balls on the Baker made guns. Only gun that I know of that was different was the Black Beauty and it simply didn't have the retaining screw.
Which leads me to notice one more thing about the gun pictured above...
The top lever is stippled instead of checked. Most of the Folsom made Leaders I've seen have a checked surface. The top lever for the Baker made Black Beauty was stippled just like the one pictured. Another reason to think it may have been assembled by Folsom from leftover Baker parts.
