Thanks for all the responses. The consensus is that it's a Williams. I did some searches and came up with a Gunrunnerjohn Youtube video of a Williams 3-rail E6s. It's a match to my engine except for the wheels (I will look more closely later to see if I can see other differences). I have attached a screen shot and a link to the video.
I admit I am a bit torn. The only other engines I have are "earlier" brass PRR. This one is later (though probably still 25 years old), so I don't know what I want to do with it. I don't have a layout; they just sit on a shelf.
https://www.youtube.com/watch?v=ujb7eLtkCaQ