I change my 315 to a 350, in my case the long shaft one. I used the plastic dish Status sell to cover the holes for the original screws and cable. Fortunately I could locate the new hole on that disc but to get the internal bracket spaced the correct distance off the wardrobe it was a touch off centre. Only problem is finding the courage to bore a large hole in the new vans roof. I got a tube cutter for my electric drill from B&Q and bored through plastic & dish roof in one shot. I made a pilot hole with a piece of piano wire first from inside to make sure it was exactly the right distance from the wardrobe wall, the the big hole I drilled from the top.
All was easy and the reception performance is excellent.