Tim,
I'm not sure what offset they are and i dont have access to the wheel at the moment, i did not request a particular offset, I only advised the type of car and bolt pattern required and they supplied the wheels and they fit fine.
The wheels are custom order anyways so i suppose they might know the correct offset that will work for the Alfa, or perhaps there is only one offset available? I would call them up, they have a website.
Early Fords such as the Escort have the same bolt pattern though so it might not be a bad idea to work out exactly what you need - make sure they make the wheels with the correct centre hole diameter. I had a friend order a set and the centre hole was too small so it would not sit flush on the rear hub, so perhaps he was given wheels to suit the escort by mistake.
Hope this helps...
Cheers
Michael