Unioncreek, what Tech says is right. Three degrees is about 5/8 inch in a foot so, looking at the engine in the car, it isnt noticeable.

When you say that all the carbs are on the same plane, you mean that the carb mounting flanges all line up if you put a straight edge across them......even if they are cut at 3 degrees, they all line up (if they are cut as a unit, not individually).

You can check the angle with an angle level.....put the level on the driveway and measure that and then put the level on the carb flange. The reading should be different...by the tilt in the mounting. (Slightly different results in San Francisco, your angle may vary, not valid in the Bermuda Triangle, etc.)