[CompClassics]

Most 5-bolt 289 Cobras utilized the C3AE-6015-N, C40E-6015-C or C40E-6015-F 5-bolt engine blocks, the casting numbers did not dictate wether the block was a "Hipo" or not. "Hipo" engine blocks were decided by stringent testing processes. As the engine block passed certain production line tests it was stamped with an inspection stamp, when the block was assembled by Ford into a complete engine it received a serial number stamping (only 5-bolt blocks received this stamp and it was in numerical sequence). From what I have researched only completed engine assemblies received the serial number stamp. C5AE engine blocks were 6-bolt engine blocks and subject to the same testing procedures as the 5-bolt "Hipo" engine blocks but were only utilized by the 289 Cobras equipped with automatics. C5AE blocks are also not neccarilly "Hipo" engine blocks, see above. Manual transmission 289 Cobras would utilize C3AE and C40E engine blocks, automatic 289 Cobras would utilize C5AE engine blocks.
If you really want to know more about the small block Ford you should invest in Bob Mannel's excellent book, Mustang & Ford Small Block V8 1962-1969.