Every whistle I've ever seen on a D&RG(W) locomotive has at a minimum a 5" base. Some five chime whistles use a 6" base. The smaller engines and the rotarys used these sizes too.
I'm thinking the beloved "Eureka" has a 5" whistle also
It does not appear to have been from a locomotive, unless it is REAL old (circa 1870?). Without some sort of documentation, I'd be suspicious.