K1 vs K2 cab w/ and w/o streamlining

[NW Modeling List]

I have a Bowser USRA Mountain.  I painted it and numbered it as a K1 while trying to create the special sand dome.  I saw a K1 picture and realized the cab front wall was sloped but not on my model.  Since it is a diecast boiler, I decided it looked more like a K2 and began researching those.  It seems to me that some K2 have vertical front cab wall and others are sloped.  Perhaps this is a K2/K2a difference..  I did find a picture of K2 119 and 123 that have the vertical cab front.  They have a sand dome more like the Bowser...maybe.
Question:  Did all the cab walls slope with streamlining added?  Was there a reason?  Were the cabs changed out or refabricated?  I hope to make a reasonable K2...
Thank you all,Mike Shockley
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