This photo shows the coach in question having a full face knuckle, this would imply the picture was made after, or very near the end, of the link & pin era. When the Janey coupler was adopted, knuckles were cast with slots in the face to accommodate links (thus rendering them more likely to break and be considered a reason to go back to the link & pin and hiring brakeman who were "careful" in their work). So, I'd date the picture as sometime after 1905.
The shadow the coach casts shows a walkway running the entire length of the car. Assuming the rail lengths were @ 30', the shadow of the coach seems to imply a length of 50' to 60'. While we cannot see the entire car end, it appears that a marker light is built into the car end and walkway If that is the case, it would have be serviced from inside the car using a set of colored glass pieces to comply with rule book instructions for rear end designation This would have been similar to the system used on several other railroads cupolas. So, I'd place this coach in the role of a mixed or local freight status. The interior likely having bunks and the other items needed to feed and house the train crew.
In 1905, the Grand Rapids line scheduled 2 passenger trains a day in each direction. One of these took @ 3.5 hours to cover the 95 mile long line, the other over 4 hours. The slower train, a daily except Sunday run, may have been mixed, though, the Guide does not indicate it as such. It is more likely it did the mail and express work.
So what I think we are looking at is a local freight, not shown in the Guide, with a coach/caboose used to accommodate LCL and occasional passengers. Public riders being such as traveling salesman or drovers or others who needed to ride with their shipments. The roofwalk was there to allow a brakeman to move over the train to get to and from his work in making up his train or performing switching enroute. Hope this helps others to fine tune what is shown.