All four of those blocks (especially the 010) were VERY common, and were used in virtually all passenger cars and trucks for many years; all were cast at both Flint and Tonawanda in high volume. Can't answer the SS/L-48 question specifically, but 350/300hp engines were made by the millions at both plants, and I can't imagine Tonawanda being the sole source for Camaro L-48 engines. Flint was the sole source for 302's and all Corvette small-blocks, but those were unique low-volume applications.