OK, after some discussion over on the UMGF thread Greg started, followed by some time with my close personal friend Google Images, I am now of the opinion that I disremembered some details, and my friend had not an F-55, but rather a GT-70; it looked sorta like a Gretsch 6120 with some Tele-like DNA in the upper bass bout. The F-50 & F-55 were shaped like an F-model acoustic archtop, but with a sort-of-almost-Macceferrian cutaway, while the F-65 & GT-75 shared a symmetrical body, with said cutaway doubled on the bass side. GTs, I have learned, superseded the F models (and were almost as quickly decataloged). Unlike the Fs they had an adjustable truss rod & colors other than sunburst (my buddy's was black). GTs had one of 2 different headstocks (one a snakehead, one a splay-sided, concave-top, 2-pointed thing), while the F used the classic Martin headstock we all know and love. Electronics were the same on all but the F-50 - which, as Bill noted above, was a single-p/up model; all the others were 2-p/up (All DeArmonds I do believe).
And I will cease my ramblage now.
Peter