Looks like an electrically driven compressor to me. Possibly 3 stage. From this angle, I see no valving on the cylinders that makes me feel that's an engine. Big hairy electric motor that critters gnawed the copper off of.
And that is a Corliss valve type as Frederick mentions. I believe that is a double acting dual compound engine. The high pressure (HP) cylinder has the steam input to it, and the far cylinder is the low pressure (LP) cylinder receiving the output of the HP side. The lower the pressure the larger the cylinder, as the far cylinder is seen in a larger housing. Records indicate the James Young company had built a rolling engine with a final LP cylinder diameter of 60". This thing couldn't be more awesome. It compressed ammonia. If anhydrous ammonia, any kind of leak could quickly kill anyone near it.
...those holes are for a crowbar to fit into.
- the bar was used to leverage the flywheel into a position that set the pistons and valve-work into a starting configuration when the engine was either, cold or shut down for some reason requiring it to be so.
The centrifugal "flyball" governor does work as you explained . When the steam engine was producing it's maximum power and the governor had lifted the balls on the governor to their maximum , it gave birth to the phrase " running balls out ". " Running balls out had nothing to do with sex.
Dude... E. St. Louis. You've got some balls, man. I've seen some of these locations in the St. Louis area while on the road. The fear of whom I would encounter was always greater than the longing to explore and take some shots. My hat's off to you, my friend. Too bad it was so sultry that day.
Like others have said, it's for rotating the flywheel manually.
Large steam engines start best from a specific position, so before starting they would need to rotate the flywheel into a specific spot. Chances are there was (or is) a mark somewhere on the flywheel to indicate to the operator where to rotate it too.
Dang it, I have seen an excellent you tube video on the fly ball governor, which list it as the source of the term "balls out" when going at maximum speed, but I did not find it in my half-hearted search.