Ah! I see what you mean, I noticed these spaces here in the photo:
Perhaps my mistake was that I used the four middle nylon bushings as spacers. Well actually I inserted them in the linkage kits holes, then removed (now realising, I shouldn’t have done so) them and used as spacers.
Looking at the instructions again, I see that I missed / misunderstood, this bit:
“Once you have tested your spacer blocks and are happy with the balance they should be glued securely to your sled.”
Thanks a lot for a quick response!