Locate a Dixie GunWorks catalog,...
in the back they have old firearms info, especially the Remington SxS, with drawing for IDing the SxS, based ob the hammer style.
Dismount the barrels and wrap a length of rope around to suspend and lightly strike with wood hammer handle and listen for a clear distinct ring.
This will inidicate if the barrels are solidly soldered together or if the top rib is loose.