It looks like the front seats are do-able but the rears are not, from everything I've seen.
I know the rear seats split different, i.e. on the Stilo the 60% portion is on the passenger side and on the Alfa range the 60% is on the drivers side.
The Alfa 156, 147 and GT are all broadly related - the 156 saloons didn't have folding rear seats, only the sportwagon. The Brera platform (159, Brera, Spider) won't work for you either.
ideally what you want are a set of cloth / fabric front seats from an Alfa 147 GTA - the black fabric should be close enough on first glance to not look silly and they're really, really cool looking bucket comfy Italian seats. They hold you like a dream. Only problem is there wasn't many people out there daft enough to buy a GTA without leather, so they're rare as hen's teeth.
The compromise would be for a set of black Alfatex (that's Alfa's name for fabric) faux alcantara front seats from a GT. The fabric is different to the cross hatching on the stilo seats but if you've got black cloth it would not look completely ridiculous. This sort of thing for £50!
http://www.ebay.co.uk/itm/Breaking-...827041?hash=item3f688a32a1:g:JvwAAOSwuzRXfi6u
And of course if you did get the rears trimmed to match it's a fabric not leather so cheaper!