your 63 looks nice, i think it's a good idea to be thinking about bags, it'll look killer. I have bags from air ride tech in my 64 fairlane, their kits are high quality, but slow (unless you get their really expensive big red system) and you could piece one together for cheaper that's much faster. If i were you i'd check out www.layitlow.com,
there's tons and tons of bagged and juiced impalas on there, ask them and i'm sure they could tell you every trick and detail in installing a system on your car. Good luck, and let us know how it goes!