My mate just bought a new standard rear diff which was supposed to be for a RWD sapphire. The flanges on the new diff are different to the old one. We tried to change the flanges but they are different lengths

What could this diff be for?

Who can reconditon the old diff? (the sun and plant gears are fooked)
How much would it cost to be reconditioned and could it be uprated for some extra money? (the car in question is 400bhp)

Any answers greatly appreciated!

Paul
Birmingham