According to Bob Mannel's Mustang & Ford Small Block V8 1962-1969, a worthwhile purchase, page 7-4 paragraph 7A2 (b) ...A second Cleveland block with the casting number of C8OE-6015-A (c) appeared later in the production year - at least as early as May 1967. The C8OE-6015-A block was actually intended for the new 1968 302 v8, but Ford's Cleveland foundry began substituting the blocks into 289 engines late in 1967 production. These blocks were marked 302 in the lifter valley (d) and have been the subject of much debate over authenticity. However, a date code pre-dating the vehicle build date would confirm the block as correct.