And if you want to carry it with your ship, it weighting 2 Earth masses is kind of a drawback.
I guess if the ship was just drifting, you'd have the heavy object at a sufficient distance to cause ~1g gravity.
I don't remember the story's title or author(s), but it likely appeared in Analog.
I was intrigued by another Hal Clement title, Trio for Slide Rule and Typewriter. I have a slide rule sitting a few feet from me as I write this, in case of emergency. No typewriter, though.
I always wondered why there's no episode where the implications of more than two dark matter engines working at once were explored :)
I really don't know how are you supposed to maintain that change long-term. But then, it's similar to the problem of deciding whether the emissions from the black hole are particles that you can focus around, so I guess it's an open problem.