green_weenie;
Visit the spring calculators here
Nova Research Project - Spring Calculators and look up the code and part number for your spring.
Chevrolet used 27 different front coil springs in 70 and 17 in 69. Unless you are interested in the front end being very high, I would look to get a spring that matches the specs of the original part number.
Armed with the spring number you can search a spring that should work for you. Eaton Detroit Springs claims to make springs off of the original blue prints. There are other springs sources too. The Camaro shared many springs with the Nova. Camaro springs that are identified part number or code should be a direct replacement. A few of the suppliers can match springs to applications. Unfortunately a Camaro spring for a certain set of options is not a direct replacement for a Nova with the same options. I have the Camaro info if you want to check the spring code to be sure.
Greg