I can speak up for the FFR. They have a new MK3 coming out soon which as an option can host the newer 4.6 sohc and dohc mod motors as well as the big blocks. The new frame is the best yet and can accept a wider 315 tire in the rear. As stated you can spend $20-50 grand building one. Mine will be around $30 when done with all new parts except for the 63 406. But that too has been fully sorted and being rebuilt. This is with me doing all the work except body and paint. But check out all the kits you can. There are some good ones out there and buy the best you can afford. No matter which you choose it's a great hobby. Check out the FF forum.
www.ffcobra.com G.