If you're running an automatic, and only on the street, you can also use an 8' from an early 60's Mustang or Fairlane. They're fairly strong and generally cheaper. But you'll have to convinve most owners that they are NOT a nine inch and not worth $200,000!  

        A well set up 8" will easily handle 300 hp. Late model 8.8's in the Fox bodies are common and inexpensive also. You'd need to remove the control arms and brackets and weld on some leaf spring brackets, but that's not impossible. If you use a 57 58 or 9 rear end, you might want to replace the pumpkin with a later big bearing unit. the '57 parts were not very strong.

                     two from"Pull-A_Part" junkyard. They are 53" from B.P.

                     to B.P. and already have leaf perches plus you can get

                     ratio's from 3.08,3.55,3.73 and 4.10. When you look at

                     the rear end tag, If there is an "L" between the numbers

                     (example 3L73) then its a posi-unit. You can get these

                      for 65-85$$ with drums or disc w/caliphers!!! The 8.8

                      is plenty tough for our Y's and they are lighter plus

                       90% will be 31 spline.... Thx Bill

PS: I did come up with a Cougar 9" for mine but will leave the stocker (3:80 posi) in until it breaks.