Any A-518 transmission Darts in here ?

First you have to figure out where your engine gets the best mileage now. Between speed and the rpm. Then find the gear ratio that will keep the engine in its happy place. (rpm)
The final drive ratio with the O.D. Math works like this;

4.10 X .69 = 2.82 final drive ratio.

If your ride likes to spin @ 2800 rpm with the current tire diameter, you will then need to find a gear ratio with the final drive ratio in O.D. To keep the engine spinning at this rpm to get the max mileage. The engine is most mileage effecient at peak torque.