You're correct - '71 was the last year of the 191 and it had two models - the Gull and the Osprey. '72 was the first year of the 12 degree 196.
The 191 is not a flatback but does have a special hull with strakes that run the whole length of the bottom and are reversed. If you look through the 191 Osprey rebuild forum you can see the strakes at the transom.