All you have to do to mount them is install 3 or 4 screws, at least on the Marlin as it is already tapped. If the gun needs to be drilled and tapped I would talk to Henry Remple or Rick at ATRS/Magnum MAchine on the north side of Calgary.
https://albertatacticalrifle.com/
Here is the link to the Skinner Henry info
http://www.skinnersights.com/henry_rifles_18.html
Appears to me that at least one of the models is a real simple self install, maybe two of them. I would call Skinner and talk to them about the EXACT model you have that you want a sight for. They have always been really helpful when I have called them.