I have used JB Weld on cracked a head It will hold for a little while. Maybe 500 miles if your lucky.
I also had the crack head welded But it cracked again right next to the weld after about 1,000 miles.
So I welded it again and after about 1,000 miles it cracked again right next to the weld. So no sense in trying to weld it a third time.
The only reason I tried to save the head was because it was special and cost me $250