I have a dim recollection that clips were used on both the frame (under the Y) and on the trailing arm (next to the slave cylinder). That's what I plan to do. I could not find any original clips but did find standard C clips that can do the job. Lots of options online.
But ...
Looking at the setup and recalling the effectiveness of the parking brake, you likely do not need the clips. The tension adjustment (the C thing in the middle of the frame box) should take up all the cable play to just before engaging the brake. This was the only way I could get usable parking brake braking. At this tension there is not enough slop to allow any of the clip locations to jump out.
Ron