A new 8" positrac carrier is going to run you around $600 or more with the ride, and you'll still have a relatively weak 8" unit. Link to Summit, for example - http://www.summitracing.com/parts/yg...view/make/ford

You might be money ahead if you can find a positrac 8.8" or 9" with track that's close to what you have and change out the mounts to fit your Ranchero.