After a quick Google image search, it looks like the steam generator equipped units had a 5-chime Leslie (S5T?) horn on the forward side. All the freight units I saw had two A-200's.
Does anyone remember some years ago seeing WIP images from Reppo of a WP GP20?
ADDITION: I can't say for sure about semi-permanent coupling, but I can venture to guess than by 1950 most roads were straying away from that if possible due to maintenance costs. Failure of one-half of a semi-coupled pair would sideline both units, whereas standard coupled units could be separated in that scenario. I can't remember when the fireman's job requirements were altered to suit diesel locomotives; the original rules required a fireman to be on every unit, which made sense with steam engines. Semi-coupling was found as a loophole in that rule until the rules were changed to suit the needs of a diesel locomotive. I should note that the original FT locomotives didn't have many "automatic" features and could really keep a fireman busy at times. Subsequent F2-F9 units pretty much tended to themselves.
I don't know the history of the B-unit headlight but I suspect that they are later additions by WP's shop forces. Straight off a steam engine
A photo here may confirm my suspicion:
http://www.wplives.com/archives/diesel/ ... s/924.html A closer look at the photo might also confirm that 924 is a semi-coupled A-B set. It was 924A, B, C, and D, but the numberboard in the photo doesn't show a letter designation. F7A numberboards from later photos and DTG screenshots show a letter A or D following the number. They dropped the letter later but by that time there were only a few units left.
Tyler