Found a photo of 3873. It is as I recalled:
https://www.flickr.com/photos/79009322@N04/16173090457/ Confirming the photo identity - I don't think they had any other EMD with that control arrangement (at the time of the photo) and the museum logo is visible on the first aid kit.
A few years ago, they acquired an xUS military GP9 that was originally an SP factory low nose. It missed SP's rebuilding program, but likely an unknown amount of overhaul work was done before it went to the Army.
IIRC - all the SP SD9s went through the rebuilding program, but many of the GP9s did not. SP never bought a late model GP9, and the switch to bloody nose paint, low nose units and 26L brake happened within a few years of each other, though SP never got any last phase SD9s.
26L first appeared in production about 1958, though it was earlier on the commuter/transit side which is where it originated. 6BL and 14EL remained an option for a while.