I just took these photos and did the sketch of the brackets that often seem to be missing from mugen spoilers, ie the piece that attaches to the bootlid, for the fella that bought my surplus kit and thought I may aswell post them for anyone else they might help.
The dimensioned sketch is traced around my actual brackets, now whether the two sides that aren't parallel here are supposed to be I don't know, both of mine are splayed similarly so maybe they are supposed to be like that
There's another bracket which attaches to the spoiler that these pull against, mine are still attached to my spoiler, so I'm assuming that's how most people find themselves.. with brackets on the spoiler but missing these ones.
However, in the interests of completeness I'll do the other ones when I get a chance.
Hope that helps