Technical leaf spring "rates"

I have been trying to figure out how to compare early Ford cross leaf springs. Having a problem getting the front spring on my 1939 Ford coupe. I screwed-up and spread the wishbones until they are outside the frame. This in turn made the perch mounts move much closer together, like 32" where the leaf spring shackle goes into its hole. So now I am trying to determine how many leaves and the arc of the spring it will need. i found out there is very little on the rate of any of the springs available from t he various suppliers. I saw where Speedway Motors said they are in the process of rating their springs, but saw a rating of 400# on only one of their springs. The springs for use on race cars are all rated and state the arc of the spring.
can anyone tell me if a leaf spring has a rating of 400#, does that mean it takes 400# of force to compress it 1"? also, it seems to me if the stock '39 front spring is sy 40" long and has 9 leaves, wouldn't a 30" spring (shorter) have less leaves and still have the same rate?
Gotta be one of you out there that has this figured out. I did talk to a real nice guy at Eaton spring the other day that said ther is a formula for all this. He didn't tell me though, and I never asked him.

 

Yes, a 400#rate takes 400# to move compress 1 inch. hope this helps:
Calculating spring rate:
Leaf Spring Rate = (WN/12) X ((1000t/L)cubed)

W= Leaf Width in inches
N=Number of Leaves
T= Thickness of 1 Leaf in inches
12=Constant for Leaf Springs
L=Length of leaf springs

 

Very interesting.... In not too long will be putting leaf springs in under the back of a 29 Model A Coupe, small block chev ,9 " rear .Do not want Coil overs Doing power turns and using high hp no longer interest in With that light of a car where do I start. ( I want a soft ride) 71 yrs old.... Have any of you with that same particular car and set up experimented or used leaf springs that you have been satisfied with? .What did you go with ?

 

Is it possible to heat and bend the spring mounts back to their original position? Those ends are forged and should be bendable like steering arms.

 

trial and error, works best in a situation like this.