changing ratios in a 9"

I just called the local rear end shop to see how much it would cost to get the gears changed in my 9" 3rd member. I currently have a 4.00, but would like a 3.50 or maybe even a 3.25. My roller is a '66 240ci.

They said it would be $750 if they have to replace bearings, $605 if the bearings are ok. It's too much for me to spend at the moment so I'd like to explore the possibility of getting a used 3rd member.

Is there anything in particular I should look for? Spline count? Input shaft?

Is there a particular vehicle I could look for in a wrecking yard that would have what I want?

Assuming its a stock Econo 9 inch you have you should look for 28 splines.

What other vehicles have 9" rear ends with 28 splines?

A lot did but heres one of several sites that may be able to help you.

http://www.fordmuscleforums.com/all-ford-techboard/468805-9-inch-rear-ends.html

I changed mine a couple of months back, you can save yourself a ton money by taking out the center section on your own and taking it to shop. I picked up a 3.00 for my 9inch on ebay for 65. and the bearing kit from a local parts store. You'll save alot in labor costs, I've never done one before,basic hand tools and internet instructions. 1500 hundred miles since rebuild and still going!