Thanks for all the replies! I am very, VERY glad I asked this question now. It seems I may have been underestimating the task and I will see if I can make some adjustments.

First, I will see if I can add another day to the trip. It will mean an average of about 56 miles per day rather than 67. I will see how this translates to real world mileage once I plot out which towns with B&Bs fall at the right distance.

Second, I will definitely work on adding some longer rides to my training over the next couple of months. I will also pack my bags with the gear that I will be taking.

I live near Washington DC, so I will be riding home. I will rent an SUV in Washington, put my bike and gear in the back, and drive to Pittsburgh. I will drop off the SUV in Pittsburgh, and then ride home.