Second, i'd suggest going over to 5.0 Tech and doing a search on 5 lug swaps...there's gobs and gobs of info over there, much more than anyone can post here to help you. There's a bunch of ways to do it...some are dirt cheap and use junkyard parts, some are super expensive and upgrade the differential and front/back brakes. It all depends on your budget.
Oh, and 5.0 springs will likely make your car sit funny, especially in the front...it would probably sit higher than usual since the springs are stiffer to support the extra weight of the 302.