Globe sights and spirit levels are period.
I think the MVAs are the most authentic but the light tight screw collar insert retainers and internal levels of the Baldwin and some others are improvements in actually aiming the rifle.
The Soule windage adjustment came out in the 1880s but I bet more Soule sights have been sold in the past 10 years than Mr Soule ever thought of.
I started in CAS single shot side matches with my .38-55 and a Marble's Flexible sporting tang and blade front. That was adequate for the 140-160 yard shots done around here at the time.
A friend got me into BPCR and I added a Lyman 17 front and Shaver Economy Soule. I later upgraded to Baldwins. That friend said: "You stayed with that cheap sight about a year too long." I had gotten to the point that its shortcomings were hurting the shooting.
I don't know if there are any limitations on sights in CAS currently.