First, thanks to everyone for the info and especially ChaseTruck for the motivation from his build and the tech way back when I first brought this up. This is my first from scratch spring build. Any criticism or suggestions would be appreciated while it is still on paper.
Here is the model of my rear springs on my frame. No CAD here, just something us old folks call "paper" and "pencils". The image is in scale, one square=2.5". With a 15 inch free arch and a 10" shackle mounted at nintey when compressed it should travel right around 20" with good springs.
The upper image shows the spring at bump, ride height, and extended. At ride height it is ten up and ten down. The shackle angle seems good at bump, ride height, and droop; the shackle angle should soften the spring rate through the travel and be anti-jacking. The spring angle is good too with some anti-roll built in. The axle travels back 2" inches at compression and forward 5" at droop giving a driveshaft plunge around 4 inches.
The lower image is just me verifying the distance of the spring at flat versus free arch to ensure the shackle is the right size. Camburg recommends a minimmum 10" shackle with these springs, and that is what I come up with spring length at 54 inches free arch, versus 64 inches flat.
One set of my junkyard springs are re-arched increasing the free-arch to 13". At 13" the spring length was 58" so my modeled numbers look good in real life. The springs were arched with a press noted in the "Ranger Rear Suspension" thread. It takes a couple of hours to do the 3 leaf pack, but I had to set up a jig. I might need to add a couple more inches, but thought it better to mount and cycle the springs verifying the numbers and preventing me from having to de-arch the springs because the rate was figured wrong. The rate should be around 250, but the shackle is going to alter that number. My math is saying the springs will compress 4-5 inches with the weight of the truck. Shackle jacking will raise it another 2" at ride height.
I may mount the front of the springs 1/4-1/2" inboard to help it track and to keep the chassis tight
The junkyard springs will be used to get everything set and if their performance is lacking the truck will get a set of 64" Deavers. I know the stock springs are not going to hold up like the Deavers, but the front is so bad that it will not be an issue for the time being.
I will get a few pics up of the arched versus stock spring packs before I re-arch the other pack.
My next mission is to figure out the shackle design and stop over at JBG to get some ubolts and spring perches.
Thanks again.