Dr Diff Offest Kit With Oval Track Springs

IDK if this will help but here's what I did
Back in the late 70s I had a 73 Swinger 318 with saggy springs. I removed the Springs and took them to a local Spring Shop. I told them to re-arch them 1 inch and add a second mainleaf, eye to eye. Those springs have gone from car to car ever since and over 40 years later are on my current 68 Barracuda still in use today. Yes they have sagged a lil over the years but I have dropped the front to match, and the car handles pretty good.
I have no clue what the spring rate might be;Is there room on the spec table for "pretty doggone stiff"?