I agree, best to find a good used lower from a standard rotation,
reverse rotation has a different carrier, reverse gear and forward gear and bearings of course.
So you would need all parts for a standard rotation, a complete lower gear set, new carrier, bearings, shims.....
I do not believe the forward and reverse gears are the same on the counter rotation as a standard rotation.
If you have ever done a standard rotation lower unit rebuild, forward to pinion is a tight tolorance and reverse gear (which is in the carrier) is almost twice as much. On a reverse rotation it is the opposite, Forward gear is in the carrier and reverse gear is in the forward (cone/bullit end) bearing,
Manual 6 should contain all proceedures.....