The number could be a C5AE-6015-E or a D5AE-6015-E, there will be no "O" in the Ford parts number system leading off for a few more decades, B thru F so far, i.e.- "C" = 1960's, "D"= 1970's and so forth.A C5AE-E block would be for a 1965-1967 289. If this is what your are reading, then the 6D18 would be for a April 18, 1966 289 block cast at the Cleveland, Ohio and used across the Ford lineup, according to Bob Mannels book.If it is a D5 something block, I can't tell you off hand.
1967 S code GT Deluxe Coupe 65B
1966 Convertible 76B 289 4 speed
Descendent of Francois Seguin dit Laderoute,
Soldier Regiment d' Carignan, New France 1665-1668