Hi Ken:
I don't have a TKO 600 in my C1, but I am very pleased with the close ratio TKO 600 in my multi use Pro-Touring Classic. Do the math and you will find that with the 3.27 first gear, and 3.36 rear gears, first will be steeper than a T-10 or Muncie 2.20 Low with 4.11 gears or even with a wide ratio 2.54 Low with 3.73 gears. So you won't go far or fast in first with a TKO 500.
I don't know how fast you plan on driving your C1, but mine is happier on 2 lane roads than keeping up to traffic on the expressway. The wind alone at 75 MPH is usually enough after 15 or 20 minutes to have me move over to the right lane at 65 MPH, which it would be happy to do with 3.36 gears. You only need a .80 OD to cruise at a lower RPM with 3.36 gears ( same as having 2.68 gears with a 4 speed). In a C1 you would rarely use fifth gear with the TKO 500 .68 OD as you would have to be going more than 70 MPH, which is when I shift my C6 into sixth (3.42 X .63).
I don't know what engine you have in your C1, but any decent SBC likes to rev, and my Pro-Touring Classic has gone an actual 160 MPH at 6000 RPM with about 450 +HP, using the THO 600 .80 OD fifth gear and 3.50 rear gears. I cruise at 2600 RPM (70 MPH) with low profile 275 - 40 X 17 (25.6" dia.) tires. Tire Diameter is an important factor, as most 15" C1 tires are much larger in diameter (27 - 29") and will cut your cruising RPM 200 -300 RPM.
Before proceeding with a TKO 600, you need to understand that it is bigger than a T 10 or Muncie, and that tunnel modifications will probably be required.
Cheers !!