Greg,
Hopefully someone will post the correct starting brace height for that bow. I don't know it and that is key to tuning it.
First, be sure that the new string is not Fast Flight or one of the other newer fibers. Use only Brownell's B-50 or BCY's B-500. These two are made for the older bows and have the necessary "give".
The length of the string will be from 3" to 4" shorter than the length from nock to nock. It will probably give you a brace height around 7 to 8 inches. A new 66" bow that I got recently, required a 63" string to get brace height right.
Twisting will shorten the string significantly. Usually you don't want start with more than 1 or 1 1/2 twists per inch of string, but when I was too lazy to build a new string, I've twisted up as much as 3/4". That's probaly 5 or 6 twists per inch. It worked, but not the best string I've ever had.
The B-50 and B-500 strings will stretch with use, so it's usually a little better to start with fewer twists, then add twists to keep your brace height adjusted.
Good luck with it,
Allen