God,the fun I`ve had with car seats and fitting recently!
To tell you the truth,unless you have a people carrier,most modern cars seem to be seriously compromised for carrying kids,in childseats.I can only just about fit my 2 year old in a Maxi Cosy Priory behind,me in my Accord Tourer whch is appreciably bigger than the 156!
It doesn`t help that the Accord has thick seats,and I need the drivers seat a log way back to get my legs in the right place.
Anyway the Maxi Cosy Priory is also used in my wifes 147,(in some ways it works better than in my Accord) and may well offer a solution.
If you are anywhere near I would strongly reccomend a trip to Milton Keynes Car Saftety centre who have helped us out several times now.We make the trip to them even thogh they are 45 mins away,because they are so much better than anywhere else.
Theres a photo on their wall showing a McLaren F1 with a child seat that they ftted so,I think they might be able to help a 156 owner!