I had a 3:55 Sure Grip 741 that came out of a 67 Dodge pickup that was an old farm truck. It was a slant 6 with a granny gear 4 speed. All I can say was when it left my place, it had a 2:76 open center, probably a 489 case. The 3:55 sure grip wasn't leaving with that truck.
Mid 60s pickups were great places to find Sure Grips with good gears, probably most were 741 cases. The 741 cases held up as well as any other center section case under the abuse I handed out. Gene