The question has been changed from the original question. However it seems people think it can be improved to be stackable. The current question itself already has an answer in a comment (and possibly another one).
At this current state, the question ask "is there a pair of monsters, that provide statblock for its living and undead counterpart?" which is basically a content identification (if my interpretation is correct). The content is already been proven by another user that it exists, and I don't think it's opinion-based, too broad, or unclear.
What this question needs to be opened?