Chirs,
Several members on this site have done such a swap. I am assuming that a "better ratio" is one that is lower numerically. Use the Forum "Search Option" to find these threads.
You are better off numerically to change to an overdrive unit (George Asche) or put in a T5 transmission than swap out the ring an pinion. If you don't mind giving up the stock third member, it might be easier swaping out your old one for a good used one with a lower ratio. The ratio you choose should reflect the amount and type of driving you doand if you are going to add any horsepower to your engine. Living in the Aschville area, I'd opt for a 5 speed.
Again please search to find the many posts on this topic.
Once you change to a 5 speed with overdrive or a stock overdrive, you will never want to go back to your 3 speed.