Thats a Solex PHH side draft carb. Similar to a Weber DCOE sidedraft. You could fit that to a TC motor, but would need another one, link them in the center, get another manifold, and move the brake booster. The manifold will be one of the easiest parts to find.
There is an ebay store that has some great carbs. Most of the time they carry 34ADF, 36ADL, and 38ADL carbs, as well as many more.
http://stores.ebay.com/ALFA1750S-CARBUR ... 513&_pgn=4
He also has a Solex 34 EIES, which looks to be similar to a 34 ADF at 1/2 the price.
That carb/maniofld will not bolt up to your twin cam head, its ment for an earlier single overhead cam Fiat engine.