On one of the first paragraphs on this page (
http://www.kirkhammotorsports.com/pricing/index.html ), the differential is listed as part of the drivetrain that is not included in the roller price. I don't see the differential on the option price list, but you can supply your own Jag rear and have the half shafts made up, have Kirkham supply the parts, or buy the Kirkham proprietary in-house Salisbury rear end with aluminum housing and half shafts at a substantial step up in pricing. If you have deep enough pockets, it is the way to go.