Lots been written about this over previous two forums.......personally I wouldn't! 6 gears in the same space as 5 physically means they are thinner and therefore will carry greater load per tooth power being equal between 750 and 1100 But the torque of the 1100 means it doesn't NEED 6 gears. So, add greater twisting force / torque on gears that are physically smaller and they are likely to fail. Some say they are fine but could you trust something that is now getting on for 35+ years old? 2nd gears in Suzi boxes are notorious for wearing the dogs - starts with a whine then jumps out ...... as its coupled with 5th you might have 4 gears to replace!