Is this damage on the bottom bracket shell concerning? Viking lugged steel frame
From here it's hard to tell if it's a crack through the steel or just in the paint. You need to take it all apart and bead- blast the area in order to clean and inspect it. It's probably too hard to tell otherwise, through the rust and paint. If you don't have a bead blaster, perhaps paint stripper and wire brushes might be sufficient. If that crack goes all the way through the steel then you will probably destroy it getting the BB apart.