I'm sure you can repair it but I would keep looking for a good one. They are dime a dozen! Why worry about one that has been repaired after you spend all the time and money putting everything together.
My theory for the cause of the cracks is people jacking the front of the motor up to remove the timing cover to change the timing gear.
I suspect many of them are cracked by dragging them on the floor.
The flywheel housing cracks can be easily repaired by metal stitching and cost less to do than buying a new one.
There's no need to take a chance with a failed part!
http://www.jandm-machine.com/metalStitching.html
If you are serious about this, I sure would be interested in purchasing 12 'good ones' from you. My experience has been that cracked ones are the 'dime a dozen' ones.
I also thought cast iron needed to be heated to a certain temp. so the weld would take, but where I work, they don't pre-heat. I work for a company that manufactures machines related to agriculture. A lot of the parts are welded cast-iron and receive a lot of heavy stress and they hold up fine. The one mig welder guy told me you have to use a high heat setting and use nickel wire. I'm not sure if nickel wire is readily available, but if I find some i'd like to try it.