Would be interesting to discuss also about any possible compatibility with Microsoft *.doc.
Wordworth 6 and 7 had RTF compatibility, as did FinalWriter97.
As to the OPs question regarding what would run on an unexpanded 1200... I (briefly) ran Wordworth 4.1 that way, but I have to say it was a deeply unpleasant experience and offered no real way of exporting files to other word processors beyond .txt.
I have to say that I prefered Wordworth, but then my needs didn't really extend to the things offered by FinalWriter.