Use this calculator:

http://www.allfordmustangs.com/Detailed/608.shtml

...and plug in the appropriate values:

5-Speed Manual (M50D-R2)
1st: 3.90:1
2nd: 2.25:1
3rd: 1.49:1
4th: 1.00:1
5th: 0.80:1
Rev: 3.41:1

4-Speed Auto (4R70W)
1st: 2.84:1
2nd: 1.55:1
3rd: 1.00:1
4th: 0.70:1
Rev: 2.33:1

4-Speed Auto (4R100)
1st: 2.71:1
2nd: 1.54:1
3rd: 1.00:1
4th: 0.71:1
Rev: 2.18:1

 

That's a neat calculator. I wish it would allow you to use tire sizes in inches, but oh well... I just used the metic size closest to my tires (315/70-r17 in place of 35x12.50-r17). my results are as expected... 4.56's to be decent all around, and 4.88's if I want to pull stumps.

Note:
to those with rims larger than 19" the calculator will not accomodate.