If it's not smooth, there's probably cancer underneath, pushing thre lead up. Grind/melt it out, and repair whatever rust you might find. There's a reason for using lead instead of Bondo- - - - -the lead will flex and not crack or peel. Sculpting with lead is a lost art, not many of us left who know how to do it. I'd reccomend against doing a full weld. Those seams were left tack-welded and filled for a reason!
Jerry
