So I found a 9 bolt BW rear that I want to put in the 91 bird. It has the crappy delco brakes on it, and my first question is wether or not I can change to put the better brakes (1LE?) on it by maybe changing the backing plate or something? Next, as far as the prop valve goes, do I use the one i have or do I need to get another one? If so, which year/set up should I use? Anything extra on the installation as far as hardware goes that I will need? Thank you guys in advance!!

Just wrapping up exactly this. You need the mounting plates, calipers, rotors and at least one of the hard lines (L) will need to be swapped or modified. Then you need the parking brake cables and brackets to connect to the existing cable. You may need an adapter or two for the brake fittings. As for the proportioning valve you can get the right one or just go to an adjustable one instead. That's the way I've gone. Flynbye.com is at least one place with a complete kit but it's expensive. I sourced all the parts myself. Not all brand shiny new but only $100 for the whole lot.

Since the 9- and 10-bolt systems, with the exception of the backing plates, are identical, you may find the following interesting:

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

You'll find info about combination valves, master cylinders, parking brake cables below:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC