Who Was "Mr Rang" in Tolkien's Letters?

In The Letters of J.R.R. Tolkien (1981), there is about eight pages worth of text comprising "Drafts for a letter to 'Mr Rang'" (Letter no. 297, pp. 379-387). I never knew there was any mystery about the identity of Mr. Rang until my friend Jessica Yates just sent me a draft of her short piece on this topic (now published here). My research of some ten years ago identified a different person.