Diff ratios can be found on two places on your diff if it hasn't lost them already through wear and tear etc.
First place to look is on the rear cover of the diff, there will hopefully be a metal tag about 1cmX5cm on one of the cover bolts, it'll have the ratio stamped on it.
Second place to look is on the drivers side axle housing, there might still be a yellow label on the forward top surface. If the label is still there and readable, the ratio will be in big black numbers at the top left corner of the label.
The last way to be sure of the ratio's is take your VIIN to the local Ford dealer and ask the service guys to pull up the original build details, (hoping the diff hasn't been changed in the car's life).