[chopper]

I guess I'll take the first shot at this. It is my understanding that the block CAN be repaired, but that the process to repair it is beyond the capability of most shops. Before the flaming starts, this is not to insult the capabilities of the repair shops. The way it was explained to me, the process involves heating the block up to (literally) red hot temperatures in an oven and then welding the block while in that condition. Welding the block in this manner reduces the temperature difference between the weld and the surrounding material, and so reduces the formation of stress risers due to the temperature differential. If this is not done, the block will crack again at the edge of the weld after a limited number of cold-hot-cold cycles. Some of this (I think) has to do with the composition of the 427 blocks, as they were cast of a high-nickel content cast iron alloy, which was different (stronger but more brittle) than the material used on the other FE blocks. I read somwhere that, after the 427 blocks were pulled from the molds, they were all stress-relieved by allowing them to cool slowly (hence more evenly) while traveling down a temperature controlled oven over a several-hour period. Even so, the original blocks suffered a rather high rejection rate due to casting cracks. I sort of recall talking to my builder once, who said he had a number of NOS blocks still in the original Ford shipping crates. He said that of every three he pulls out of the packing, one has some sort of crack in it.

I offer this as an interested bystander, certainly not as a materials or welding specialist. Perhaps George Anderson or one of the other long-time engine building gurus would help out here.