If you do the math, you'll find that (unlike a purpose-built truck auxiliary transmission) you have a theoretical total of 8 ratios, but some are so close together as to be useless.
Example, using .70 OD:
1st 2.84
1st OD 2.00
2nd 2.01
2nd OD 1.41
3rd 1.35
3rd OD .95
4th 1.00
4th OD .70
Look how close 1st OD is to 2nd, 2nd OD to 3rd, 3rd OD to 4th: they don't do anything.
Using a close-ratio box:
1st 2.56
1st OD 1.79
2nd 1.81
2nd OD 1.27
3rd 1.37
3rd OD .96
4th 1.00
4th OD .70
Still nothing...
