Style/macros for outlines in Plain TeX

Question

I'm seeking a style file or other macros for creating an outline in Plain TeX, of the traditional indented style, eg.

I.  Big Idea  
    A.  Sub idea  
    B.  Sub idea  
        1.  Thought  
            a.  Sub thought

I'd love to write one (some day) if no one has done this yet, and if anyone might be interested in collaborating.

Answer 1

(Made CW answer from comments)

These Plain TeX macros are vintage 1991:

http://homepages.rpi.edu/~sofkam/MTeX/mtex.html