Mike,
Welcome to the wonderful world of Cobra people.Picking a manufacturer is difficult and it depends a lot on what you are trying to achieve and what state you live in.
If you want a Cobra that looks like the originals with the correct wheel offsets then the CR is not for you as it uses donor parts that prevent this.The CR is pretty easy to put together and with the number of CR owners on the forum you wont have any problems. The CR has a well built chassis and the body comes with all panels glassed in. Makes it a great bath tub.
If you want to go racing then the Harrison would be hard to beat as it is probably one on the lightest and you get to try your sheet metal skills as well. You also get a pretty good wheel offset as well.
The best thing you can do is join a club, go to the meetings and ask lots of questions. I wish I had.
Its also important you talk to your engineer and find out what is and isnt acceptable in your state as the rules change and individual engineers have different interpretations.
The easy way is to buy one already built, especially if you have your heart set on a Ford engine and are trying to avoid the Dark Side.
What ever you chose you are in for a blast.
Phil