C16 Pumps

Hi Guys
A friend and I are working on building 268 and 278 in 1.20.5 scale. We are building a number of components and the present project is the Westinghouse pumps. An article in the Narrow Gauge and Short Line Gazette stated that both 268 and 278 were both fitted with eleven and half inch pumps, but studing photos 268 pumps sure look a lot larger than 278. So what size pumps are they now fitted with in their preservation?
When you model someting you sure home in on details you wouldn't have noticed otherwise.
Not only did the pumps get wider, they also got taller, but the compressed air part also changed.
There is the version with the ribbing that would act as cooling fins, then there is those without which I would suspect are the steam engine part casting used for the bottom [air] end. Would these details relate to the different sizes?
I thank you for all your help
Michael Hilliar