If your chain is at all old, I would consider getting a new one installed as well.
thanks for the advice. it's relatively new. i had had the 12/23 on for all of this year until about two weeks ago to prepare for a real hilly ride. i brought the entire bike into the shop and wasn't sure if they had adjusted the derailler. today i need to have the 12/23 put back on but only want to bring in the rear wheel.
Worst case scenario is that you need tiny cable tension or set-screw adjustments to get it smooth, although I wouldn't fear any issues to begin with. Chain length and tension shouldn't be an issue as you have run this set-up before if I read you correctly.