K27's always had the pump in the left side ahead of the cab. Initially they had one 9" pump, later 2 - 9", then finally 1 8-1/2" cross compound.
The C16 and C19 came with one 8" (?) pump in the right side, but by the 1900's had one 9" on the left side. Eventually they got a second 9". The last C-class engines in service recieved 11" pumps in the 1950's.
While it is a good idea to have both pumps the same size, it is not necessary. Somewhere I've seen photos of an engine witn both 9" and 11" pumps.