Mark - why didn't you tell him the application is a 56-58 motor w/ dual carbs? sounds like a little lack of communication on your part, is he supposed to make the assumption that you have a non-49 motor because you have a Rochester carb in your hand?
carb parts are very specific, and the tag is important as 5 different B's may all be different, and tagged so, and if you're convinced you have C's when the carb expert says there is no such animal, how can he be expected to know what you need?
as others say, I've found carbking very informative and helpful and had you presented the complete information, he no doubt would have had a viable solution
Bill