Could you fix it? Yes. It's not terribly uncommon to see old welded Chevy 348/409 blocks or Mopar Hemis. I have no clue on the longevity of the repair. But in order to do it, you have to pull the motor, clean it, and heat it a bunch before you weld it. If you wanted to keep the truck numbers matching, it may be worth trying, but it a 4cyl Comanche, I don't think it is worth the work and I would swap in a different block.