OK, here is my response PRRronbh -
The MTH Southern F-3 version is the as delivered scheme from late 1948. Both the 4173 and 4174 were originally built in 12/48. They were classified by EMD as F-5s, though Southern called them F-3s. They have an F-7 body, but F-3 prime movers and traction motors. Since MTH did not put dynamic brake fans on them, they can be used to represent the 1948 - 1952 time frame, since both 4173 and 4174 received dynamic brakes in mid 1955, and are in black, not green. The smaller lettering and numbers in front of the cab ladders were Southern style during this period.
These F-5s were not used for passenger service since they never had steam generators. They were painted green by the early 50s, which all Southern wore regardless of service. PS-1 and wooden boxcars, wooden and steel reefers and two-bay hoppers would look great behind these units.
In comparison, the MTH Southern F-7s just released represent the 1959 - mid 1970s scheme used on F units by the Southern. The nose herald was removed, lettering was larger and the number was moved behind the cab ladder. These were always used as freight locomotives as well.
I thought about buying the F-3s, but waited on these F-7s since they can be used for a longer period of Southern history (if you want to represent a true modeling era, otherwise, run them as you wish).
MTH made these F-7s in part due to the NS DAP units, since they are the same scheme with different lettering. It is my hope MTH comes out with F-3 (F-5) or F-7 Southern units in the green scheme in the not too distant future.
I hope borderman01 I have not burst any bubble for you. I have been a big fan of the Southern Railway for quite a while, and have both O and HO models of their F units. I like the 1956 - 1960 period in HO, and look for similar models in O as well. As I said, they are yours, and you can run them as you wish, just giving the actual history of the units.
For passenger, you could always find the MTH Southern PS-1 F units, painted in the original passenger scheme, though their body styles are not totally correct.
An BTW PRRronbh - I am back at Spencer Shops as the interim director at least through March or April, so I might see you at the hobby shop sometime.