Arnolt Bristol Front Spring Rates

[412usa]

Does anybody have any experience with having springs re-tempered. I would like to do this for 3020 but I'm not sure of what information the spring rebuilders would need.
From Ken Oakes notes on his calculations for the 404X projects he states that the front spring rate is 81lb/in per wheel with a frequency of 75 cps. This is not too far from the article in the Automobile Engineer article on the Bristol 400, which stated a total spring rate of 250 lb/in for the front spring or 125 lb/in per wheel with a frequency of 83 cps. As the spring shackle is the base of the spring I think the spring rate and wheel rate would be very similar.
Thoughts would be appreciated.
Peter