Before splurging on those wheels, your will need to make sure they clear the drums on the rear.
There has been a fair amount of discussion here about it and the final determination was that "It fits on some trucks and not on others, you have to try your individual truck."
I haven't tried on my 39 yet. I forget who tried but didn't fit, but I am sure they will chime in soon.
Do a search and you will find plenty on how to check your ratio.
Its a pretty good chance your high is about 6.17:1 and your low is about 8.10:1. This is about a 30% jump (or drop) essentially splitting 3 and 4 on the granny 4 speed. Many people will say it is a low speed to help you get a load moving (and that is how I normally use it), but in fact it also allows you to drop to 4 low instead of shifting down to third when climbing a hill (I use it for this also, but I'm not as good at the downshift as I am at the upshift). Hope that made sense. The 2 speed rear allows you to split gears to stay in a better power band and keep rpms down, but it takes some practice to do it.
