For the 1969 model year (if I read it correctly) and you go by the Chrysler parts books and sales literature, the 225 cyl got the 7 1/4 axle and the 318 got the 8 1/4 axle with a 2.71 gear ratio. If you wanted a lower gear with/without suregrip, it would have been the 8 3/4 axle.

I own a '69 318 Coronet parts car with a 8 1/4 and I parted out a '69 318 Coronet years ago with a 8 3/4, so I've seen them both ways.