Take a look at the nice KBD of the 1400 for your hack.
I haven't looked into the rear section of the top deck issues yet, but I've been toying with the notion of grafting (just barely }

) a 1400 KBD onto a Duo. It's an exceedingly tight fit, but looks eminently doable in terms of trimming back the sides of the the top deck bezel, you might have to file the edges of the outboard keys a tad, but the wonderful metal chassis appears to fit without a problem.
I'm not sure about the feasibility of removing the function key row if it conflicts with the chassis or vice versa, but it might work out. I've got one disassembled that's been fitted to the shell of BabyPB, my first laptop, a remaindered PB100. I can dig it out and look at the circuitry. IIRC I was thinking about making new contacts to rearrange the matrix to match outputs, but getting it back together looked problematic. The color contrast looks fabulous, BTW, especially with nicely yellowed plastics.
edit: I just pulled out the boxes:
1) the front edge is still several times less flexible than the Duo's and ought to be fine if the back return is removed.
2) it looks like I can get a KeyCap off without breaking it, but I haven't figured out how to get it back on without borkage yet, so . . .
. . . reassembly using flat head machine screws in tapped holes drilled in the chassis appears to be out.
3) by scoring the chassis using a pointed bit on a router table and bending/fatiguing the function key section off looks like the best bet
4) scoring and snapping the plastic section of same is very doable
5) the flex circuit is a folded, one piece design, so it can likely be bent up, over and between chassis and top deck
6) it'll take some convoluted bending, but the flex cable looks like it'll stretch to a connector nestled under the video cable to the left side of the useless modem connector.
All in all, it looks very tight but good to go. The controller board from the right ADB KBD might fit in the modem bay and be tapped into ADB on docking connector. This would be perfect if you con't need to loose the function keys and a lot easier than getting the KeyMatrix signals to the Duo's MoBo. There's enough space in there for a matrix conversion setup as well, given the right controller. [}

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