Rear Leaf Spring mod with Durango Springs

I did nearly the same thing as you. I junked out a couple of A bodies, mostly for front disk parts. I tore down the springs, and the springs under my 67. I simply put the longest leaves of both original spring packs from the junker and the 67 back in the pack. I believe I have one more leaf than stock, but they are all the longer leafs. The thing sits just right. I hope to get the disk brake front end under it soon, which will also mean AT LEAST a front sway bar. I may have "enough stuff" to manufacture mounts for rear bar as well.