I talked to Kim Flowers at the railroad this morning. Her answer:
1) It is an RGRPC train, not a Friends Train.
2) Dan Ranger has not decided yet whether the train will run, and it is his decision, based on motive power, cars, etc.
3) The reason he has not decided is that Sept. 23 comes right in the middle of the 'Cattle rush': the busiest part of the season. Unless 484 or 488 comes out of the shop in time, the motive power may not be available.
IMO there is enough doubt about the status of 484 and 488 that I would not make plans to take that trip.