Thanks Jackofjr. I dont have the car yet - still waiting.....its going to be agony. I spoke with Piranha, they basically said come in and they will sort it out, either by adding links to the smaller size, or (probably easier) removing links from the larger size.
Nissan assure me that you can get the chains on the front wheels - although I have my doubts, as you say, there isnt alot of clearance in there.