The whistle most likely came from a B&M Mogul or Pacific. When the railroad was scrapping them at their Billerica shops, there were literally piles of bells and whistles, headlights, number plates, etc. lying around. Anyone with any "connections" could have gotten some, probably for a bribe of some sort. Most of the whistles have B&M cast into the fitting somewhere.
Years ago there was a wonderful sounding steam whistle at the gelatin plant in Stoneham near the old Stoneham Branch next to Route I-93. It was mounted on the boiler house and was sounded several times a day. A friend did some research, visited the boiler room and was even allowed to blow the whistle by yanking on a long chain that went up through the roof to the whistle.
Later on, after the whistle was no longer used, we got in touch with the engineer at the plant and he said we could have the whistle if we would preserve it. At the time, I was the curator of the Walker Transportation Collection, so we assured him the whistle would be well taken care of. Long story short, we got it and had it cleaned up and placed on display. It looks real good, and I believe has 6 chimes. B&M is cast into the base of it, along with a casting number. The plant engineer said it had been given to them many years before by a B&M employee. He had told them the whistle came from Boston & Maine 4-8-2 #4108, "Lilly Pons". We compared the whistle to photos of the 4108 which showed the whistle, and it appears to be a different type. People say the 4100s had "steamboat" type whistles instead of the usual multi-chime variety. So, who knows? It's a great story. It definitely IS a B&M whistle, but beyond that, we are not sure. At least it got saved.
Richard