The plot is very similar to the Season 4 opener: The Vaqueros (1961). In that one, Lucas and Mark were assaulted by Mexican bandits and Mark was kidnapped.
Both part 1 and part 2 were written by actor Robert Culp. He had appeared on the series twice, but these were his only 2 writing credits in the series.
In the McCain house, there is a rifle above the fireplace. It is a Sharps rifle. It shows up in other episodes, too. There is an epi where the bank has a large amount of money in the safe. Expecting a robbery, the manager puts a man with a rifle in a back room that looks out into the bank. His rifle is the Sharps. Another epi is in a ghost town, a former mining community. Mark sees doors closing on their own and one scene has an unknown man standing with a rifle, the audience sees it from his POV, looking out at Mark and Lucas, maybe Micah, too. His rifle is the Sharps. The rifle is not the carbine, it has the full wooden forestock.
Though filmed for the time period of the 1880's, Lucas is wearing Wrangler jeans that weren't invented until 1947.