True - only 2 available for the 208. If you need something else you'll have to make it from a 700 gear or something. Typically if you use a reasonable gear ratio you can get the speedo right just by changing the driven gear, which is like a 5 minute job. (What, you can't find a low enough tooth count for your 44's on 3.08s? Good- that should never be done.)
So the easiest way to do the math is grab a GPS and drive at a normal cruise speed (like 55 or 70). The ratio of your real speed to speedo reading is the same ratio you need in tooth change. The driven gears are color coded, too, and even have the tooth count stamped on them sometimes. All you need is a 1/2" socket and the gear is in your hand in 30 seconds. If your speedo reads too low, you need fewer teeth on the driven gear or more teeth on the drive gear. Of course you won't swap the drive gear unless the tooth count you want for the driven isn't available.
If you use the online calculators, find your real tire diameter instead of the size stamped on the sidewall.
That being said, you might want to wait on speedo calibration until you have the right gears in the diffs. With 35's and a 305 you should be running something more like 4.56 -but that's another topic.
