I'd ask for the GT person to not just provide services one hour per week but to train the teachers in what your DS needs. The GT teacher should explain what level your son is and then help the teachers to find appropriate material and integrate it in his day.
ITA. I'd also not discount what the school might be planning to do until you've had the meeting and heard what the plan is. Remember that an IEP meeting isn't a "happens once and that's it" type of thing - it does happen once to write the IEP, but if the IEP isn't working, you can always request another team meeting to update it. Sometimes updates can be made without an official meeting if all of the team members agree.
Next thing I'd be sure to do before the meeting - find out everything you can about your school district's gifted services. It sounds like you are already fairly familiar with what's available but find out everything you absolutely can through both reading school district website, policy, state gifted ed policy (if there is a policy in your state), and through networking with other parents and teachers. Note: this doesn't mean you have to expect to *settle* for what is typically offered, it's just important, if possible, to know the possibilities out there and the box within which the school district might try to fit him.
You can also request a copy of your ds' test scores (actually I'd just request a copy of *all* of his school records) in writing, specific the test name and that you want the complete report), send the in to either his school office or the district administration office. You can also request to see the test scores before the meeting via email. The school staff might not *want* to provide you with the scores, but I am fairly certain they have to provide a copy if you request it.
Best wishes,
polarbear
