The joint is there due (educated guess not original knowledge) to having to form the sheet metal in several pieces. I see no reason you couldn't make the patch as you described. If you're a good welder and body man, why not go ahead and seam weld the whole joint? I made sure they put a good fill of seam sealer on mine before paint.

'69 1/2T stepside, Sea Foam Green, 250 L6 w/ 3 on the tree, not an option on it, in the family since new.