There is now a complete kit to convert to 6 lug disks. I just
bought one on ebay.
Here's a detailed web site on
installation I guess it probably uses the 4X4 rotors Brian mentioned. I'm sure it would be cheaper to scrounge your own parts and buy the bracket kit.
Buffalo Engineering doesn't have a site yet but on their future site I noticed another interesting item; an adapter to run a 350 tranny behind a 248.