I repaired a small crack on my MGA with JB weld and ran it that way for 12 years of so. I swapped the block last summer and had the old one welded as a spare. I cleaned the weld and covered it with JB weld just for good measure. Make sure you clean it with a wire wheel or something to get all of the crud out. If it is in an area that you can work on without much trouble try it. If it doesn't work put the other motor in.
