My rear is to low

[LONGHAIR]

You will need a new carrier, the Posi unit that the PO installed will not work, but you don't need to replace the entire housing. Even so, this will be an expensive swap to do it like you want.

Posi differential..............$400+
Gears...........................$200ish
Install set.....................$100
Labor varies by location...$150-$200?
Bottom line.....................$850+

For that kind of money, you could swap in a 700r4 and gain the overdrive.
Or you could swap the entire rear end, housing and all, for one with higher gears and sell your old one. You would should be able to sell the complete 4.10 unit for more than what a junk yard unit would cost. The down-side to that is in the "posi". Even if you happen to find one, it will probably be that boat anchor called "Gov-lock"....you don't want that, especially behind a big block.

All of this "assumes" that we are talking about a 12bolt rear end. If this is a HO52 .........ignore. As far as I know, 4.10 is the highest gear available for them.