Breakaway backrest conversion!

[cormyb]

Wondering does anyone one on here have the backrest conversion. I have the old one but bought a new box which you cannot open fully with the older backrest.
If any one here could tell me the length of the red brackets that fits to the box. Want to make up so spacers to make it fit so I don't have to fork out for a new one.
I would measure myself but I'm stuck at sea at the moment, but have a full workshop here to make up some new ones.
Cheers