Wow Horror ,
There's something to think about , are you saying that the distance from the front eye on the spring to the point where the axle is mounted is different ?
Now if the lower shock mount is on the lower spring retaining plate then it would be raised by the difference between the thickness of the original spring and the thinner replacement ,perhaps an inch ? Now as i expect to raise the rear of the car by again an inch then the installed length of the shock would remain the same . So i don't anticipate any issue there but i am concerned re the length from front eye to axle .
BTW i do have cable opperated handbrakes
Dave