i have bad news, that looks to be right on the split of the case halves, and welding it is gonna make it tough to get the 2 halves to seal properly, which will cause an airleak and go boom again
you can't just weld a piece over it or you'll never be able to split them cases
i'd say new cases are in order,
you still need to pull the intake and pipe to get a look inside to see if the piston skirt broke, or if it was caused externally by a rock or whatever ????