If your transmission is a C4 there should be a tag on the driver side of the tranny on the servo cover. For a 1968 289 it would be PEE-C1 the Id Number, a service number, a assembly part number, and a built date and shift code number.
If it was the transmission from a 351 it would be a FMX transmission. All 351 Mustangs 1969 and 1970 had FMX trannys and the tag is on the driver side also but the ID number would be something like PHB-E , PHB-H, PHB-E1 or PHB-P plus all the other stuff on the tag like the C4
Since your block is 289 I would think it is a C4 like Jim has stated but if the pulled the tranny from a 351 Mustang it is possible it is a FMX and since it would fit someone might have thought the motor was a 351 and put on the emblems. But this is total speculation on my part. I would have to see a picture to be sure.
The C6AP-70027-B number has me guessing but it is most likely a C4 just from the cast number, The pump body casting number is useless in determining the year as the same casting number was used on most pump bodies from 1964 through 1981.
Here a link which might help id your tranny http://www.crankshaftcoalition.com/wiki/Transmission_Identification