As for cracks between valves, This is typical of the early gas trucks to have happen after overheating the motor. Choices would be to have it repaired with weld. These usually last indefinitely if done correctly. The welder should be careful not to make a pile because you really don't want to grind down the excess weld material because this may cause it to crack again in that area. There is no reason not to have it repaired unless it cost more to do then a wrecking yard replacement or new. Wrecking yard replacement usually will require rebuild or at least machine work.