I would like to share my observation of this block. The reason they used a 618 block with a March casting will never be known, and very unusual. I have an 05A car with vin 19n6401xx and a stamp of V0430DZ and a 010 block. Two other examples of 05A are 19n6404xx with V0425DZ, 010 block; and 05A with vin 19n6403xx with stamp V0430DZ and a 010 block. It looks like the block in question is completely out of wack with standard procedure. It looks like the stamp date should, at least be in the first week of May with a vin in the 643 range. There are several known examples with vin's in the 639 range, with a 010 block. This block may be good, but the GM worker was drunk!