The pads are more shaped to the metal plate that bolts around the leaf spring. By that I mean...
'73 and earlier plates use a round hole that the rubber pad sticks through, and the plate welded to the axle sits on. It keeps everything lined up and straightened out when everything is together, so the axle doesn't slide on the metal plates.
'74 and up pads/plates use an oval shaped hole on the plate, and the pad sticks through that, finally with the axle resting on top of it all, keeping it all straight just like the 73 and earlier ones, just a different shape hole for the axle mounting.
I know this because I put a '73 axle on my '78 sedan but I couldn't make the oval shaped pad and plate fit against the axle's round hole mounting plate. Since the situation was only temporary (until I got the 8"), I bought a set of top plates and pads from Fred, and used my '78's bottom plates with the correct shock mount. I never had any problem with things setup that way either.
You may be able to modify the '74 and up pads to fit your axle/spring plates.