So to confirm:
Your retina images are 86x64 (the ones in that thread are, so if you took them from there, you should be fine).
You've got TWO copies of each image. They are named EXACTLY as below, right down to punctuation and caps. Double check this, because in your first post "balloon" isn't capitalized and frankly this is where I tend to screw up myself.

(screenshot taken via PhoneView from my phone just now)
These four files are in a theme in Winterboard;
they are in a folder called: Bundles,
in a subfolder called: com.apple.chatkit (Again, watch for caps. This is another place I screw up. Tried to theme something yesterday and forgot to make a "Bundles" folder for it, LOL)
That theme is available in WB, is at the top of your list, and is checked? Uncheck, recheck and respring again to be sure, once in a while things take a second go round to appear. Also close your SMS app out in the multitasker and reopen it afterwards in case it's using a cache of some sort.
If all that is true, and you're running 4.2.1 or above, then please post screenshots of your setup in WB and iFile, because something's decidedly weird. The only other thing I can think of is you may not need the 2x files if you're on a 3G/3GS--you didn't specify your model phone. But Apple includes them for all models, I believe, and the system *should* pull the size you need.