Last month I was in Michigan, and brought back about 500-600 old family slides. I searched some forums on whether I should ask them not to be xrayed, and the consensus was that is was fine - having already been processed and developed.

There were four rectangular solid Montgomery Wards metal cases, plus some sleeves in cardboard boxes - all inside a big duffel bag. Surprisingly TSA at GRR didn't even ask to open the bag. I was going to alert them it might look odd but things were going fast and didn't even get a chance. But I'd allow extra time. Where are you flying from? At some airports (like Denver) there are multiple checkpoints so if you're declined you can just go to a different one. Also if these are in a large carry on make sure you're early boarding or small enough you don't have to worry about full overhead bins.

Have fun with your project. I rented a professional slide scanner over the July 4 weekend, made more sense to pay $60 for a high quality one than spend $100 for a crummy one at Best Buy that I'd use one time. And while it took many hours to do I love seeing and appreciate old family photos, especially our old family cars and clothing.