Replacing the leaf springs probably won't help if puts the rear end in the same place (vertically). I would think that if you put the car on a lift you could look underneath and see where (exactly) the rear end is hitting the body. If it's hitting where the u-joint is located then it's your pinion rising too far "up" (pinion angle). If it's hitting on the top of the center section then you simply don't have enough clearance for that differential with the body as low as you have it. You need to determine "where" the differential is hitting before you spend any money attempting to fix the problem. It should be obvious where the rear end is contacting the body. I've had similar problems and I always put the car on a lift to see where the rear end is hitting the body. You need to identify the exact origin of the problem before you start drawing conclusions.
PS - If I remember correctly you've already looked under the car and you said that the yoke/u-joints are rising up and hitting the body. If this is correct then you need to verify your pinion angle to see if (maybe) the pinion angle is set too high?? Even if you replace the springs it won't change the pinion angle?
treblig
