The turnkey minus cars for $57,000 do include the complete rear end. All you need to do is to supply the engine, tranny, clutch, pressure plate,
oil cooler, if you want one, and all the little bits and pieces. Most Kirkham owners opt for an FE, but I think there is one gentlemen on CC that comes quickly to mind that has a small block in a 427 car.
You can talk to the Kirkhams about deleting the rear end and you can source a Jag rear end from some company like Terry's Jag Parts and save money. I'm just guessing, but the aluminum rear end from Kirkham is/was $5,000 and a complete rebuilt Jag rear end is probably in the neighborhood of $2,000, but check on that price. I'm sure it can vary. The aluminum rear saves about 45 lbs, if that matters to you.
Tom Lucas from FE Specialities built my engine as well. I'm happy. I've heard Smeding builds very good engines, but he doesn't do FE's as far as I know. There are also many happy Keith Craft customers too.
Good luck with whatever you choose.