Editing Identify and date Borg Warner transmission

Looking for help with my 1969 Olds 442 post coupe. Numbers all match EXCEPT the trans. My understanding is that this 400 cid V8 4-spd. came from the factory with a Muncie [? M-20 or M-21]. Mine has a Borg Warner with the following identifiers cast on it:1304065903, below which is : W.G. DIV., below which is FpC1 with the p and c set lower.Could the experienced out there please a} cofirm this is NOT original equipment b} suggest when it was made +/- the earliest it could have been swapped? Any suggestions as to whether it will stand up to hard driving/hole shots, and [Canadian if possible] sites to get a Muncie  would be gratefully accepted. Thanks, Derek