New Holland T2310 (40hp), Kubota L3010 GST, New Holland TC21DA *** Previously - Farmall H, 1941 John Deere B, Shibaura SD1500, John Deere 850, Bobcat 642, New Holland 1925
I had a John Deere 850, and it was a tough, reliable and capable tractor. Pictures of the crack would give us a better idea of how easy or difficult the fix will be. Pictures of the tractor will help assess the value.
It all depends on where the crack is. Since this is a sleeved engine, you stand a better change. It's still a bit of a gamble.
I had some luck patching cast using a silver/nickle/copper brazing rod. Cooling it slowly is absolutely required. When brazing works it is as good as new. I've never tried welding cast.
For brazing or welding you want to take it to a master.