I am building up a 1983 300SD, performance injection pump, intercooling, different turbo etc. I want a highway runner that I can get some mpg out of, like 2000rpm at 70mph instead of 3000 range. What diffs fit back there and what ratios exist, I need to pull the rear axle shafts anyways for boots etc I would like to swap the diff too. I plan on building the car so it has power at lower rpm, my direct injection VW's and smart make me want to...and would like to get better economy out of the benz, it is hard to drive it when all the other cars get two or three time the mpg...