I went from a 7.17 single speed rear to a 6.14/8.36 2-speed and gained about 10 mph. The truck (1957 10500 Fire Engine) would run 63/64 mph all day long at about 3800 rpm...if I pushed it to the governor it would run into the high 60's.
You'll be happy having the donor truck to get all the little pieces from as you swap it over.
Keep us posted with pictures, I'm interested in seeing how it all come together for you!
Mike B
