I needed to get a new driveshaft for my Camaro as well and listen to the above advice.
Something else to think about when ordering a new shaft is u-joint size. I got all my stuff from a company called Shaftmaster's and they supplied me with a 3" x .095" wall, steel driveshaft with 1350 joints on each end.
Your 9" might already have the 1350 pinion yoke installed so you might as well get a slip yoke for the P/G made for a 1350.
Dave at Shaftmasters told me to measure from the tip of the tailshaft on the tranny to the tip of the pinion yoke and he figured the rest out. It fit perfect.
If I recall mine cost right around $300.