I contacted the NCTM, and here is what I found out:
Event: July 3 & 4 (Tuesday and Wednesday)
Shoot Schedule: Each Morning: 6:30 - 10:00 AM
July 3rd Evening: 6:30 - 8:30 (not sure if would go later)
Advance cost is $25, $30 day of event if tickets are still available
Tickets are advance sale, starting Monday, May 21, 2012
There are no NS heritage units coming for Rail Days, June 2 & 3. They will have the N&W GP30 to pose with SR GP30 2601 for the 30th Anniversary shot.
I do not know if there is a maximum number of tickets available. To order, call 704-636-2889 starting Monday and ask for the July NS anniversary shoot. This was just announced yesterday to the staff.