Unless it's pouring coolant, don't sweat it. That weld is at the bottom of the water jacket, a common place to get a crack from not running enough (or any) antifreeze. Somebody has done a pretty good job of welding- - - -"pretty" doesn't count, it's whether or not it leaks that matters. Leave it alone until you have a reason to tear it down to a bare block, then do a little grinding to improve the looks and add a layer of Marine-Tex if you're worried about the possibility of a leak. While the patch is curing, press a piece of 40 grit sandpaper over the repair to match the surface roughness of the surrounding cast iron. After a paint job, the repair will never show.
Jerry
