Vario Top Box adaptor plate - HELP!!!!

[Dave56]

I`ve just bought a vario top box + adaptor plate that was fitted by the previous owner in place of the pillion seat.
I now want to fit it conventionally to the rack but the term "square peg into round hole" springs to mind.
If you notice on the photo below I assume that I have to remove that central peg - but what am I to do with the two plastic legs. They appear to be part of the locking mechanism for the top-box yet don`t allow the plate to sit square onto the rack.
Am I to remove them, if so how.
Appologis if this is a "numpty" type question but any help would be gratefuly recieved.

 

[The Bede]

... See if this helps (sorry it's in Sausage!)

 

[boxster]

you will need to get the rack support bar (item 4) as well

 

[Dave56]

I have the support bar + all the bolts etc. It was those pins which were causing the problem. Thanks for that Boxter & The Bede.......