I did this yesterday with my 110v MIG.
It isn't the prettiest, but it will hold just fine. The top one I had to grind, I didn't leave enough room for the bead . The bottom one I spaced better and left a groove. It filled in pretty well.
This is DOM steel, .120" wall x 1.25".
This is a removable bar above the transmission to facilitate removing/installing the engine and trans together. It's a Vintage Spyder, but not mine. Just linear compression and tension on this part of the frame, no bending or twist loading.
Oh, and I highly recommend 3M Scotch Brite Clean and Strip discs to clean the mill scale and weld slag off the workpiece. It makes priming and painting a piece of cake.