No you can't remove the rearsight to mount a sight. Well you can remove the rearsight but the rearsight mounting bit is actually part of the action, in other words there are no rails behind the loading port.
You can mount a scope but the only mounting area is that little section in front of the loading port. You could use two mounts pushed together on the scope body for extra rigidity. See my thread in Sales; that's a red dot but same principle could apply to a scope.
“We are too much accustomed to attribute to a single cause that which is the product of several, and the majority of our controversies come from that.” - Marcus Aurelius