question about switching gears?

Never heard the balancing thing before. If we are talking an 8 3/4 you can use the same carrier for all of the gear ratios. But since I have not heard of a 3.10 gear in a mopar what rear do you have? I have seen your posts on the different rearends.
You can't just "bolt" in a new ring and pinion. The first and most important would be the pinion depth. If you don't get this right then the other required things just will be a moot point.