Here's a photo I acquired of Union Pacific M-23 believed to be in Callaway, Nebraska. M-23 was built in May of 1915, weighed 37 tons, and was the first all baggage McKeen Car. The car was builder's number 146 out of 152, and purchased by UP for $22703.12 in 1915. This was the first McKeen Car with a McKeen built 300HP engine. I believe through what research I've done that there was a carburetor on each cylinder (the engine was a straight 6) to help reduce resistance on the intake side the engine. A single carburetor supplying fuel to 150 liters of engine is a big task. This however would nearly prevent you from ever tuning in the engine as you would have to pick out, by ear, which cylinder was not firing right and how to fix that carburetor.
This photo was taken before 1934 when it was painted in the Famous Union Pacific Yellow and Brown paint scheme of the streamliners. This was after the pilot was replaced with flat sheet metal, possibly an attempt at further streamlining this car?
The trailer car behind M-23 is T-18, one of two early McKeen Cars to be rebuilt into an unpowered trailer. T-18 was originally UP #7, the first round window McKeen built in March of 1906.
At this time, both cars would be in Pullman Green.