Keith,
I have been watching Otto Perry's San Juan Express Video tape lately. 478 is in it quite a bit. There is even a shot with 478 and 484 on a freight train as that particular day the San Juan was sidelined to get this freight around.
Earl Knoob was posting the daily movements last year. It seemed that nearly every day of 1950 and 1951, 478 and 484 were assigned to the San Juan. I guess people's camera were lucky enough not to catch the 478 on film.
If you can find the Otto Perry Photo Collection on the web, you'll find a lot of 478 on the San Juan there.
Kevin Cook