To start out, you dont need or want to change your crossmember. You only need to change the spindles out on both sides. Up until recently the using 71-72 or 73-87 spindles and disc brake parts were the best option but left you with 5 lug rotors. You could have your new rotors and bearing hubs redrilled for 6 lugs. I know this option works very well from seeing it done many times on the 60-66 Chevy and GMC email lists.
But more recently I have heard of using spindles and rotors from a 1990's light duty 3/4 ton would get you 6 lug. But I dont have any more info on that right now... Not sure if it works or what parts that it takes.
