The word of Mr. Narlow and Mr. Voigt are good enough for me. However, it wouldn't really surprise me if interest in Rick Marshall as the Zodiac continues to resurface. The handwriting business seems to be on-going. In the movie Vaughn takes credit for the printing of the posters, or was that just a twist by Graysmith and the screenplay writers to steer interest away from him? The most consistent description of the Zodiac is that he was 5'8 to 5'10 (Michael called him 'short) and around 200 pounds. I believe Rick was 5'7 and 200 making him closer to the Zodiac in body size than Gaik, Kane or ALA. Other than that there doesn't seem to be much else that recommends him.
I think years ago Tom jokingly posed the question on one of the threads if Rick and Gaik were the two members of team Zodiac? I took it as a fun tease and satire. The obvious answer was 'no.'