I got a chance to buy some 426 Hemi heads. Both heads are showing cracks near the spark plug holes. One head, all four are showing cracks, the other, I could only see 2 cracks....are these repairable?? What would their value be once repaired?? How long could one expect these heads, once repaired, to last?? The last three on the part number on one of the heads was 559.