I had terrible luck with National Carb a few years back. They have a great guarantee, but who wants to keep pulling carbs off and shipping them to Florida?
After repowering a few years back, I held on to a real marine Quadrajet that I had rebuilt locally about two weeks before I decided to repower. It's still wrapped up in a box in my garage attic.
Where are you located? Maybe we can work something out if your close.
If you want new, I would consider the Edelbrocks as previously mentioned. My new motors came wth them, and I like them a lot.