I’m no expert but it’s probably a fantasy scheme. Although the dairy may have existed. I live South of Boston. Back in the 60s. Many local dairies delivered milk in bottles from their own cows. The grocery stores all carried Hoods. My wife has heard of Buttermilk Bay in Plymouth. If there was such a dairy. It would have been served by the New Haven. The only cars I know of that interchanged between the B&M and NH were the White Brothers cars destined for Quincy MA. Just south of Boston.
I model the Rutland. They originally served NY City. The only cars in there consists were Sheffield Farms, Bordens, and Dairymans League. When they no longer could go to NY they started shipping to Boston. You would see Hoods and Whitings. The most colorful car in my opinion was the Atlas Brookside Creamery car. The Rutland switched the creamery in Bellows Falls but the cars traveled on the B&M to Boston carrying already bottled milk
Good luck building your milk train. Definitely one of the most interesting trains that ran as a scheduled train.
