Like Bob says, you have to consider the mono leaf perches. Not only are they not as deep as the multi leaf spring perch, they also don't have the hole that the center bolt sits into. When I was hunting for new springs, I saw Eaton had a 126 pound spring rate three leaf spring, mono leaf replacement that had the center bolt peened flush to fit the mono leaf perch. I was going to buy those for my 68, which has a mono leaf 69 Camaro rear, but the cost of getting them to Pender Island was out of reach. I bought five leaf springs, drilled out the center of the perch to take the center bolt and welded blocks onto the perches to extend them to fit the springs.

I'll add a pick of the perches with the hole drilled. I ground the tip off a 1/2" drill once the hole was through the perch and used it to flatten off the bottom of the hole, similar to a bottoming tap. Can't seem to find a pick of the blocks welded in.

You may be able to use the same lower plates/shock mounts.