The 7.17 will be the "high" gear and it will have a 9.75 "low" gear ratio. You don't want that rear, it will be slower than what you have now.
I took a 7.17 out of my Fire Engine and installed a 2-speed with 6.14/8.36 ratios and gained about 10 mph. The truck will run in the low 60's all day long.
Mike B
