Rob,
You do not need power steering in these cars. The power steering rack, usually from the Mustang, it FAR too twitchy for highway driving. Good for autox, but at speeds above 50 mph, you better not sneeze, or you'll be two lanes over.
Power steering also lacks feedback. If you want it to be as "close" in handling to your 'Vette as it can be, skip the power rack. If you want around 3 turns lock to lock, your only choice really is the 15:1 Flaming River Rack. It will be slightly harder to turn in parking lots, but shouldn't be a big deal. The only time I can imagine it would get tedious is if you were parallel parking it. And I don't ever recall parallel parking my Cobra yet.
If you want, you can come on back out to my place. We'll take my Cobra to the high school around the corner and I'll let you run it around the parking lot (sorry, like I said before, my insurance won't allow me to let you drive the car on the road), and you can feel my steering at low speeds. My car has the 18:1 Flaming River rack, but also has 17" wheels and sticky tires.
Steve