One of the other guys is looking at doing a similar thing, and it sounds like you both may be looking at the same carb on eBay. Check with DavidATX. Make sure you don't get into a bidding war.
To answer your question, though, unless you also make some cam changes to take advantage of more airflow, you won't be using the Q-Jet to its full potential, but it will work.
I don't have the Rochester specs on the small-valve 455 carb, nor the 68 350 4-BBl carb, so I can't be certain, but It probably will need to be re-jetted and tuned to work on an otherwise stock 2-bbl motor.
