Changing the mass of the driveshaft will NOT affect performance, it may save a kilo or two. As to gear ratio in the 8 inch, my best compromise is 3.25 on 14 inch wheels, with a lot of torque you could pull anything up to 2.8:1. However the 8 inch is two pinion and may fail with enough torque. You can get LSD which I would advise.A little off the topic of engines but I have read where people have used an aluminum driveshaft out of an Explorer in their early Mustangs. So that will held get a little more power to the wheels. Any body have any recommendations for good 8 inch gear ratio for street use?