There is a product called Lock N Stitch that we used to fix 2 cracks in the block of a Super 77 Diesel.  It worked good and is not too hard to do.  When you get done you can run a needle scaler over the are and it is hard to see where it was patched.

Do a search for Lock N Stitch and see what they have on their website.  Not the cheapest, but cheaper than taking it to get it welded.

Bill Brandt