Early Pintos had a small hole about 1/2" in dia. Then from 74 or 75 the 6 3/4" and the 8" from Mustangs  II went to an oval cutout in the spring pad. This was done so better soft pads would fit and remove vibration coming from the rear end. There is a couple of ways to get around this problem. You can make a plug out of 3/8" aluminum, the same shape as the oval cut out. Put a 1/2" hole in the center and your done. Put the plug on top of the spring, lower the rear end over it and your done.  Aluminum plug can't come out because the rear end is on one side and the spring is on the other side.  Other way is to weld an oval shape plug into the spring pad.  It will also need the small hole in the center. It's really easy to fix and VERY necessary to keep the rear end centered with the car. I've done it both way and they work the same. The weld way works the best if your going to use lowering blocks.

That should work really good. Good work.

Another thing I've done is if your using  a 1" lowering block and if the bolt that goes thru the spring has a head say a 1/2" tall, I will place a dowel pin the same dia as the spring bolt head and just long enough to stick above the lowering block about 1/4" and fit into the spring pad.  I tried using a 1" longer bolt thru the spring and lowering block but they kept breaking, so I tried the dowel pin and that fixed it.