I don't have a ton of experience as much as some of these other guys, but my opinion would also be that a brake swap would not be a good bang for your buck in terms of weight loss, assuming you don't need better rear braking performance (I have a really hard time believing you would unless you're road racing or something). The other reason you gave was availability of parts. That really concerns me, honestly, because I'm wondering what parts you're looking for? I did some internet searches last night for a lot of the 11x2.5 parts and had no trouble finding anything. If you're relying on AutoZone for your parts, that's your big issue. You're dealing with a 30-40 year old car, can you really expect a chain store to tailor to your needs? Especially when you're dealing with a car that has non-stock brakes on it, normally intended for a different application. Do yourself a favor and do searches for C-Body rear 11x2.5" brake parts (whatever you're looking for), at more appropriate vendors, THEN tell me you can't find parts for them. A little bit of research and poking around could save you a lot of $ for other things. If you're really that scared, once you find the parts, buy a couple or a few for the future, and you'll still have a lot of extra money left.