Any idea what size and ratio's the diff's are in a sierra xr4x4?

been given the chance to get the diff's out of a mates car but wanted to confirm size and ratio's first.

im believing they are 7" but been given the impression that they are 3.9 opposed to the 3.62 that an escort cossie runs!

Any one able to confirm/agree with this or put me write about the sizes they are

Cheers
Kelvin