Re: Further RG F-unit Q *PIC*

Mike, I hope you don't mind me extending your NNG thread just a bit with a Rio Grande F-unit question of my own.
In the years the Grande operated the RG Zephyr, motive power was commonly an FA-B-B lashup, with the converted Alco steam generator mixed in. In every picture I've seen of the Zephyr through those years, the converted Alco was always the second or third unit in the lashup, never the last as I (admittedly pretty doggone ignorant of diesel operations) would expect.
Anybody know why? Pure chance, something related to how the units were serviced, or some technical reason?
Here's an example I shot from one of the domes on a trip in the spring of '79.
Scott