I'm with Jerry on this one. If the "born with " block is gone, IT'S GONE. The most correct thing you could do is to find a correct casting and dated block as a replacement. Even if you found a MU block it would be difficult to have it also date correct. Possible, but very hard. It would still have an incorrect vin on it. The only thing better would be to deck it and restamp with your vin and production date and MU. I know many people out there have a problem with that and I appreciate that aspect also, but that would make the most correct restoration,( as it came from the factory) which is what we all strive for, right? It's a shame that the honesty factor sometimes looses out to the almighty buck. When these car's weren't worth so much it wasn't much of an issue, but that's the times we live in. By the way on the MO block issue, really the blocks are the same, came from the same foundry, are machined the same, only that stamp is different. I'm pretty sure I am correct on that and please correct me if I spoke in error. Well i'll get off my soapbox now and everyone have a happy holiday!