The springs were most likely the stock BB springs that would have been used with the Super Sport L78 cars. These were "converted cars"...starting life as a 4 speed L78 and then Yenko upgraded them to the 427 motor. Chevrolet made the spring selection based on options a car had that affected the weight on the front end. The springs were basically the same as a 69 Camaro...codes were most likely HJ or HH... this chart will give you an idea of what I mean. Perhaps Greg Roberts has one specifically for Novas.
http://camaros.org/images/pages/chas...ring_chart.pdf
I have checked the spring tags on several original L78 Novas...everyone has been HH.
I believe Eaton can make you the exact springs you need...I have ordered from them before. Perhaps some of the other tech gurus have other suggestions.
wilma