I'd say. yes, it does look like the rack for a 550.
The racks mount at upper shock mount bolt and the bolt that supports the side of the rear mudguard under the seat.
The distance between centres for a 550 should be approx 175mm, for the front 'prong' and the lug on the chrome tube.
I modified a '750' rack by welding two new lugs to match my 550.
I then made up an adaptor plate to attach a Givi monolock plate & topbox (not very 'classic' looking, but functional)
It worked a treat for the Classic TT trip last year:
http://www.sohc.co.uk/index.php?action=dlattach;topic=6171.0;attach=5544;image
