The only difference would be the sway bar mounting tabs (if it has them, most dont) 73-76 is different from 72 and older. Aside from the sway bar mounts they are all interchangable from 67-76 regardless of brake style or size.
The 73-76 sway bar passes through the K frame and is narrower, the mount is near the bump stop on the LCA. The older sway bars bolt up under the front of the K frame and have the mounts out near the ends of the LCA under the strut rod. The older bar wont work with a newer LCA.
Should be a simple matter of drilling the holes in the later K frame under the strut rod mount if they're not already there, and bolting the factory mounting brackets for the 68-72 style bar on. Makes sense if you've got all the bits for the 72 style bar.