Dodge Dakota rear ends....

What is the power output intended for the Dart and is it a true street car or will it be used in "Spirited" driving?

The reason is that the 8-1/4 is cheap, very, by compare to the 8-3/4. The smaller rear will handle 400 HP & TQ no problem. However, if your going to push past that and drive it a bit hard, the much more expensive 8-3/4 is what you want.

The 8-3/4 took my buddies all steel 500 cube, 69 Dart into the mid 9's. The street gears within did eventually break after many many pass's pulling up the front wheels.