I got the most complete Quadrajet Rebuild kit I could from Cliff Ruggles, and it just replaced my stock idle tubes. From what I recall. the key point in his book was to make sure the tubes are not plugged. I don't remember much discussion about using a different sized tube.
I don't have Ruggles's book handy, but can try to find my copy if you don't get any better answers to your question.