Going from a triple to a single is quite a step. I assumed you were going from a double to a single.
But yeah, with the remaining ring on the middle position, chainline should be good.
I'd be in no hurry going to external BB. They tend not to last as long as square taper, and the supposedly increased rigidity have never impressed me.
But if you insist, do get the shell faced. Bearings not entirely perpendicular to the axle is suspected to be a considerable contributor to short BB life.
Don't worry about the weld, the tool can deal with that.