Hmmmmm. Well.... it MIGHT be a 6 chime. That's a standard D&RGW 6" base and valve. Someone might have gotten an SP or ATSF 6 chime bell and stuck it on there. There were some odd duck whistles on the NG over the years. This might be another.
I should point out the D&RGW never had a 6 chime on an engine as a "company whistle" The D&RGW cast up 5 chimes and made hoots.
At one time the practice was that freight engines had hoots and passenger engines had chime whistles (3 or 5 chime) Real early on there was a longer bell "passenger hoot". Later one this got all mixed around. You see all kinds of 3 and 5 chimes on T-12's. K28's came with 5 chimes (despite being originally intended as freight engines), the K36 & 37 came with hoots.