IIRC the dealer doesn't set by numbers, they just use a gizmo that gets close enough to give them a go. I could be wrong and they are actually setting them now by numbers.
Now is the time to go with a RamAir. That is all I have and I wanted to check it for cracks so my TBs were very easy to get accessed.
I am pretty sure you will need the tank raised, I just put the cluster back in place and held there with one of the front screws. I can't think of any other reason it threw the code other than the cluster was off. When you say air box I believe you are talking about the plenum (grey box on top of TBs). I am pretty sure it has to come off to adjust the TBs, I don't see how you could access the adjusting screws otherwise.
bob