I think it is very possible it could have been factory made...but not a regular production item offered by the company. I worked for a rather large window manufacturer up until a few years ago
This company had their catalog of products....but to cater to the whims of the major customers or to win over a new prospective customer they would make nearly anything they asked for. To keep accounts they would custom make at a loss some exotic items. I cannot see why this could not have happened in the pump manufacturing industry back in the day also.
Another possibility is it could have been customized by a buyer for a paticuliar station application. Would not be that costly or difficult to do by a local metalworking shop.
These are my thoughts on some definite possibilties, but no way to know what this pump has been through in in its 80 year life.