I grew up in the area, and still frequent the location. The former site of Westchester Yard is eaily visable from the Weiler Hosptial of the Albert Einstein College of Medicine (built in th early 1950s) west of the former NH Harlem River branch, now Amtrak's NEC. The yard was bounded on the north by Pelham Parkway, the eastern boundry would be approximately where the Hutchinson River Parkway runs. The southern boundry was Waters Place, dividing it from the New York Subway's Westchester Yard.
The last physical remnants of the yard were about two or three of the steel catenary support towers in what had become the parking lot for a Fuel Oil distributor on Waters Place, near the corner of Eastchester road. They lasted until about 2003-2004 when the property was sold and ands a new Pathmark Supermarket was built on the site.
I recall watching Penn Central RS3's shuffling cars in/out of the siding to the Old London plant (also the home of Dipsey Doodles, not just Melba toast), as late as 1974, which still stands adjacent to the NEC tracks. I beleive that was the last of any freight activity there.
It seems the Westchester yard was sold off piecemeal. Looking at the photograph in the first posting on this thread, if you can imagine you are looking northward at the yard while standing on Waters Place, the land on the right hand side of the photo became the Bronx Psychiatric Hospital in the 1950s. while the the land to the left was split into three distinct pieces; The southermost section of the former yard (on Waters Place) became the storage and parking lot for a Fuel Oil Distributor (and now the site of a Pathmark supermarket). Above that (north along the NEC tracks) was buikt Calvary Hospice in the early 1980s. And north of the hospice stands the Old London plant. My guess is that coal and fuel were delivered to the fuel oil distributor via some remaining trackage in to the 1970s as well.