Ouch... Is it that bad on both sides? I know this is a little beyond what JB Weld can fix, but you could most likely fix it with some Alumaloy and a propane torch, the key to that stuff is the part has to be CLEAN and you gotta keep wire brushing it clean as you heat the metal up to 700 degrees, best measured with an infrared point and shoot type thermometer.
The engine will also need to be removed and you'll need to get all the fuel and oil out of from inside the case.
The other alternative would be to have it MIG or TIG welded, but in that case it might be cheaper to buy a new bottom end from DAX as he sells the really nice balanced ones for $69.99, these are the ONLY bottom ends I'll use when building a performance engine as they're very smooth and rock solid dependable if you decide to go that route...