The retaining cap bolts into the existing holes for the dust shield and holds the bearing in place, as the grooves for the clips are machined out. The wheels sit no further out than normal, it was all measured/calculated and machined so.
Made up by Race Engineers who have run Vectra's in several 24 hour races, could of gone all out and adapted the awesome ones they built for their Vectra, but they may of been a bit overkill!!