I actually just got done investigating this very issue cause my old C-4 is the 5 bolt type. 5 bolt bellhousing only use 5 bolts to bolt directly to the engine. They stopped making 5 bolts around 1967 or 68. The newer c-4`s use 6 bolts to bolt to the motor, and did all the way until they stopped making them i`m geussing around 1982.
I got this info from a guy thats been running a tranny shop for long time, I hope its right. He wouldn`t rebuild my old c-4 cause he couldn`t find the parts or the bellhousing to convert it to a v-8 bellhousing.