i have dell'ortos 36 on my 1776 engin.
the guy who adjusted my engine told me, that dell'ortos or webber 40 were better.
if you plan to buy some used carbs, be aware, if they are modified for a use on a vw-engin.
if they are still prepaired for alfa-engines, maybe this link can help you for the right settings
http://cgi3.ebay.com/ws/eBayISAPI.dll?ViewUserPage&userid=alfa1750