Considering how overlapping the floors for Kestrel A and Kestrel C are, I decided to take Lord Trilobite's The Kestrel greebles, and create ones for The Swallow, with a help of some greebles took from broken ships, and custom-made pixel art. Incidentally, the "inside" part of room-less Swallow sits just next to Life Support system, so I decided to follow my own advice

and created it the way, that it's looking like inside-ship part of said visible system parts. The result is quite satisfactory (
Edit: Updated 28.07.2014) :
http://s10.postimg.org/tkihtwx89/swallow.pngWhile doing it, I've also noticed few micro-glitches in original Kestrel A greebles (some random dots in outside-of-floor area, made by mistake - surely no one would notice it in the game, anyway), and I've also added few structural reinforcements and other odds and ends, where I think they were lacking. Then, I took .append files created by RAd-82, and packed every available greebles (Kestrel A tweaked by me, unchanged Fed Cruiser and Stealth and new Kestrel C) and packed it into .ftl file, ready for installation:
http://www.mediafire.com/download/pabgbk3tn6ztklm/greebles.ftlHappy flying with greebles, for me, they increase FTL experience quite a lot

They're working fine for CE too, obviously. Sadly, no Slug Cruiser files here, as Trilobite haven't released his WIP file, and separating it from his in-game screenshot - while possible, as it is in native resolution and .png - would be too much time consuming.
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Now, considering that A, B and C variants are, in most cases, different versions of same ship (example: all Kestrels), I think that best approach for creating greebles, would be to take room layouts from all of them, overlap it in GIMP - leaving ONLY the part, that overlaps in all three variants - then, create greebles for whole ship, EXCEPT the part that is covered by floor in all three cases. This way, one greebles file could be used for all three variants, with only minor modifications needed.
There are few minor exceptions (Crystal'ish Rock C, for example), which would require completely different greebles - although, those are complete minority (is there any completely different ship variant, other than Rock C?...).
Cheers,
/Estel
// Edit...aaaand, the file from last post got silently updated, with even more detailed version of Kestrel C greebles. This time, every "always will be there" system that is next to greebles got "rest" of stuff from system images displayed at greebles, not only Life Support. The latter got fixed to, now it show the rest of this big pressurized 02 canister, and I aligned everything else, better than last time (thanks to getting in-game screen, and placing it as overlay over greebles image that I was editing - IMO, it's best way to create and edit those greebles, as you see exactly what systems it is next to, so you can make ship insides look more coherent with in-room systems).