My favorite set of carbs. Had a set of 36's on my old 1300 and setting up a pair of 42's for the type 4 lump. 40's will be fine for the 1600.
Go to Amazon and buy this book [ame=http://www.amazon.com/Weber-Carburetors-HP-Books-774/dp/0895863774/ref=sr_1_1?s=books&ie=UTF8&qid=1337779460&sr=1-1]Amazon.com: Weber Carburetors (HP Books 774) (0075478637744): Verlon P. Braden: Books[/ame] and this book [ame=http://www.amazon.com/Weber-Carburettors-Tuning-Tips-Techniques/dp/1855207591/ref=sr_1_2?s=books&ie=UTF8&qid=1337779460&sr=1-2]Amazon.com: Weber Carburettors Tuning Tips and Techniques (Tuning Tips & Techniques) (9781855207592): John Passini: Books[/ame] . Then go here [ame=http://www.piercemanifolds.com/category_s/308.htm]TECH HELP[/ame] and read up on the setup and initial idle, and depending on how worn the carbs are, order a rebuild kit for both of them.
I love DCNF's, though I'm a little biased. I learned on those carbs and they fit perfect under the decklid with the shorty manifolds (you'll need Type 3 manifolds to go with them) and a 1" air filter. Like any other carb, there are far too many variables with tuning to get into here, that's why I'm suggesting to purchase those books and rebuild kits. You'll likely buy a half dozen or more different size jets for both the idle and main circuits just trying to tune it correctly, so budget for those as well.
R