"Guild had an F series too, if I remember rightly."
Indeed they did. I had an F-20 once, a lovely little guitar (my first good steel-string guitar), that was made so early in the Guild history that the peghead was Gibson-shaped with a decal, Martin-style, instead of the plastic overlay of most Guilds since then.
And Mississippi John Hurt played an F-30 sunburst, as I recall.
The biggest Guild F-model was, I think, the F-50, a jumbo that often was made in maple as well as rosewood -- the maple F-50s were really nice guitars.