That was my first tune ever
. I wish I could tell you something better than mess around, try different things, and try to come up with a number close to that, but that's all I remember doing.
I'm pretty sure I started with lowest top speed and max final gear, so I'd suggest that first.
Then, depending on how close that lands you to the range, increase or decrease the final gear each time you "Flip" the transmission to get closer to the range.
Alternatively, you could give it your own custom transmission numbers for whatever kind of race you want to do with it.