I've done it. It works. The big difference between the 11 and 13-inchers is that there are a series of chips _under_ the blade SSD on the 11-inch, whereas the the 13-inch is just empty space under the SSD (in order for there to be room for the double-sided chips on the blade itself). I'm not sure if they're RAM or whatnot (I have my doubts, since their size and quantity don't seem to change between 2GB and 4GB models).
At any rate, you can put the 256GB SSD in the 11-inch, but the four chips on the bottom of the blade are going to be in direct contact with the aforementioned series of chips directly on the logic board. I tried the installation with a piece of electrical tape between them to try and mitigate any heat issues, but that caused there to be an uncomfortable amount of flex required in the blade module in order for it to be screwed in.
At any rate, I'm typing this answer on an 11-incher as we speak, with a 256GB SSD and nothing seems to be blowing up quite yet.
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