I do Fairlanes, Falcons, Mustangs. My personal car is 63 Fairlane.
I wouldn't waste my time $$$ dearching springs.
1) The best solution is reverse eye springs. The front eye is centered to the spring, and the rear eye is reversed. Readily available from Mustang suppliers.
2) Cheapest = Lowering blocks increase the leverage on the springs that will increase wheel hop. You should clamp the front spring leaves to reduce the hop. Make your clamps out of 1/2 steel and use 3/8 inch grade 8 bolts. Actually, just clamp the leaves on ANY FORD.
3) You can safely use a rear shackle that is one to 1 1/2 inch max shorter. That will give you about half that much drop at the wheel well. Make them from the long lift shackles (70s) cut off excess, weld the bolt heads into the shackles)
Always use urethane bushings at each end. They really help the wheel hop. I noticed no ride/noise difference.
Also if you have a wheel hop problem and your car is equipped with rubber spring isolators where the spring u-bolts to the leaf, eliminate that. That raises your car about 3/4 inch, but the height can be adjusted as explained.
My car has custom built springs, no blocks or isolators, and then had to do # 3 to get my desired height, and still clamped my leaves. (I hate the look of traction bars hanging down)