Welcome, glad to see another IH/Farmall owner.
While the block could be repaired, it might be cheaper in the long run to find a used block/engine and do a rebuild. This way you would have a rebuilt engine that should last a lifetime if all you are using the Super A for is hobby and goofing around.
At the family blacksmith shop, we've seen alot of cast items come in. Although we have fixed them mostly because they were family heirloom kind of items, my Dad and I have told the customers that it won't be the same in strength.
The biggest problem we run into with welding cast items is that it must be extremely clean for the weld to take any kind of hold. As you said it has been sitting for some years now and has obviously oxidized and for it to be an inch long crack, that makes it extremely difficult to get cleaned. The other thing to cast metal welding is you have to get it really hot before welding and then let it cool down slowly.
You would be having to disassemble the engine anyways, so you might be better off doing like I said earlier and and finding a different engine and rebuilding it. This way it is a fresh engine with the same structoral strength as it left the factory.
