This is the phosphate-coated LS MID sleeve kit from Darton. While eight sleeves are needed there are actually three part numbers here: the four in the center, cylinders one and eight, and cylinder numbers two and seven. The sleeves for LS1 (Gen III) come in two bore size ranges. The smaller set covers from 4.125 to 4.160 inches while the larger goes from 4.170 to 4.200 inches. For the Gen IV blocks there’s just one part number that covers from 4.125 to 4.200 inches.