Some of the little, inexpensive Marlin, bolt action rifle receivers of that time were grooved for mounting a telescopic sight, but your gun is not one of them. So, to mount a telescope, you would have to drill and tap the receiver for a scope mount. This will take away from the original condition value of your gun. These guns do not have a great collector value as yet, but drilling and tapping will affect any value it currently has. If it were me, I would get the proper receiver sight or parts to complete your rear sight and go with that. This little rilfe has the old style Ballard rifling and will be extremely accurate without a scope.
From your pictures, the butt plate and grip cap are not original to the gun and have been added at some point. They will not have much affect on the overall value at this time, so you can leave them alone for now. The original butt plate was a flat, black plastic butt plate and the gun did not have a grip cap originally.
I hope this helps.
Due to the increasing cost of ammunition, there be no warning shot!
The growing federal deficit = generational slavery to the national debt.