Re: Further RG F-unit Q

well i think you are close but the set they ran was a-b-heater car-b the reason for not having the other A unit on the train is so that it looks more "streamlined" and because cab units for various reasons need more maintinece...
and the reason for having the b unit on the end may have been used for turning the units easier if they had to do a backup move B units were equiped with a very rudimentary controll stand next to the door on one end (having never been in a B i cannot with conviction confirm) if they turned the units at a roundhouse or a wye it might have been usefull... on the other hand it wold have meant you had to cut off steam if the units needed to be changed and the steam car would need MU lines and connectors.
very weird