Diff ratio's

Get in touch with Central Coast 4x4 Wreckers. They have a very large range of parts, old, new and reco.

Easy... take out the old diff assembly, take it to a gearbox/diff specialist and let him know the new ratios you are after. $600-800 per diff later you bolt back in your new bits.
Removing diffs means taking out your axles- that may mean simply taking off the hub studs, or maybe taking out the whole drive flange and CV assembly from the front to get at it.

On what car?

Supply and fit?

Genuine gears?

Tight arse job using old seals and bearings?

Or you want it done properly?

Where are you?

Will you be doing any of the work yourself?

Are you fitting lockers at the same time - if not why? Save $100's doing it this way since the centers are all out anyway.