That looks like Locktite where the mounts were. You can remove it by heating to about 280* with an electric heat gun and using some steel wool to wipe it off. Watch out for the wood when you heat the locktite.
After it's cleaned off, get some plug screws to fill the holes, if you're not going to scope it.
A red-dot sight is a very nice piece for a lever gun to be used in the woods. The Bushnell mini is close to the smallest available and you can get them for under $100. Batteries are supposed to last 3,000 hours of operation. I have mine on a handgun and it's a bit small for dot acquisition on it, but would be fine on a rifle or shotgun.
“God save us from people who mean well.”
― Vikram Seth