i found this from a june '71 bulletin #2. outer: 110lb @ 1.83", 276lb @ 1.36"

inner: 31.5lb @ 1.56, 50lb @ 1.13"

cab, do you remember these old yellow springs? sure wish i'd kept some of that stuff.

if using an old 300/308-.520" lift grind you don't need a bunch of spring. it's a pretty gentle profile. the issue will be using a stock steel retainer with a more modern 1.50 and larger diameter spring.