I believe I understand you better now. The thing is, why is an external crack causing smoking. No one has been able to answer that yet. I think the crack is also in a cylinder(s). I don't see why risk getting stranded or running parts I could otherwise sell off this motor.
Keep the welder... It's like "Wear Sunscreen"
No you misunderstand me... I think you should fix the crack and drive what you have and drive it for at least 2000 miles before arriving at your final decision. ( I personally think it's going to clear up by then)
As said above while you do that look for a replacement and rebuild at your leisure. If you can pick the next motor up while it's still connected to a decent truck body then BUILD THAT at your leisure as well. (you'll need that welder then for sure)
