I would not know about the specifics of the Viper, but getting the jib right is very important even for a selftacking rig.
Both the setting of the car and the sheet helps determine best angle of attack for the jib. We always looked at the two in combination as oversheeting and undersheeting is very easy while the perfect trim is hard to keep. The good news is that you can probably get away with three or at most four settings for the jib car. Very low wind, low wind, medium and strong winds. At least we did, and it is a very common way to do it. Hopefully some of the other Viper guys would know the "class standard" settings. Or perhaps we could get some values from the different boats and sailcuts? Usually these are measured from the center of the track as the tracks might vary in length between designs.