Additional help or comments...
I purchased a #1, s/n 4001, .222 rem. It has a 26"" medium barrel, no sights, drilled for scope blocks, but the unusual thing it has what appears to be a factory installed quarter rib. I say factory installed because the locating pins are installed as well. From what I have been told, most gunsmith installed ribs omit the pins.
I talked to Lee, the #1 GURU, and he gave me more information than the gentleman at Ruger did. The only thing that Ruger said was that the quarter rib could have been installed at time of mfg.
Has anyone else ever heard of this configuration?