Gears & Axles - Drive shaft length?

Ok i have done a search is the factory driveshaft the same is one for a 6 speed with 9in. Or does it need to be longer or shorter with the 9in.

I have not installed mine yet, but the one Billingsley Racing sent me appears to be the same length. He had me measure my stock one and said that he knew what length I would need, and it appears to have been the same length as the stock one.