If the scope mount is good and the rings are for a common size putting a good scope on it would be the fastest way of getting it back to a shooter. I saw no traces of filled screw holes for an original sight. If the dove tail is a common fit, any number of good sights may be available. Using an original SA sight would entail drilling and tapping new holes or finding the originals and removing the plugs.

Many here do not mind revealing the serial number, the number might be helpful in knowing whether this was an original 1898 carbine. There is a current list of 98 carbines being compiled on KCA. So far there are less than 20 of the 5000 or so originals known. I am not sure if the list includes heavily modified sporters or not.

If this was an original carbine it might be worth looking for a box of parts that were removed, many times the original parts are found in a corner or somewhere. Carbine rear sights are worth more than a pretty penny.