The cars are indeed on a 1900 chassis. There were TWO seperate versions of this car built!
Gulp model in Italy makes both versions, the green and the grey car. The grilles and some other details are different!
Check their web site at:
http://gulpmodel.interfree.it/ They also make miniatures of other interesting Alfas.
I will eventually be stocking them here in the US at my new web shop:
http://sites.onlinesupplier.com/folder61925/