Summary

Updated part info and replica (printable) original case for self-supplying the parts for the MakerBot Gen4 Interface Kit.

Instructions

Since my ToM pre-dates the G4IK, I never thought I would want one. But my workflow for printing from the SD card has become increasingly tiresome (especially with Sailfish), so now I want one! Sadly, there's no kit available, so it's time to DIY!

First, order a PCB from batchpcb (pcb#79131, thanks to TheMakerGuy's thing:18416). (It's fully possible to protoboard or hand wire, but batchpcb provides a great service.)

[2013-07-03] Since thing:18416 is gone, bobc has graciously put up thing:110911 as a replacement.

Here are the part numbers and part cost (as of 2013-02-24) from Mouser:

1x 16x4 character LCD (668-NC-S16400XFGSAY; $16.09/ea. There may be other NMTC equivalents for cheaper, but they may not be the right dimensions.)
9x B3F 12x12mm std tactile switch (653-B3F-4055; $0.375/ea).
9x B3F switch keycap, grey (653-B32-1300; $0.25/ea). There are more colors; check the other 13xx parts.
2x 20-pin IDC socket, 3M (517-8920; $1.03/ea).
1x 20-pin IDC header, 3M (517-30320-6002; $0.57/ea)
3ft 20-pin ribbon cable (shielded/rounded: 517-3659/20FT; $1.47/ft. Basic: 517-3365/20FT; $0.38/ft).
2x 5v LED, red (696-SSLLX5093HD-5V; $0.27/ea).
2x 5v LED, green (696-SSLLX5093GD-5V; $0.25/ea).
4x resistor, 1kOhm (291-1K-RC; $0.054/ea).
9x resistor, 10kOhm (291-10K-RC; $0.054/ea).
1x trimpot, 10k 1/4"sq (72-T70YE-10K; $0.80/ea).
2x 8-pin, 8" .100 cable (538-28100-0335; $0.25/ea). two, to make 16-pins!
Feel free to order larger quantities to "save" on cost; there's bound to be things you can do with 50 resistors, extra buttons, or wire!

Hardware parts (from your parts bin, local hardware store, part supplier, amazon, etc):

4x M3 x 16mm socket cap bolt
4x M3 x 22mm socket cap bolt
8x M3 nut
4x M2 x 16mm socket cap bolt
4x M2 nut

While you're waiting for shipping & delivery, print the case.

The case is designed in OpenSCAD (polygons imported from the original DXF). I've added built-in spacers and hex cutouts (which probably don't save plastic overall, but looks cool).
Each part is split into halves (to fit a ToM build), with an extra set of mirrored side STLs. The way the parts have been halved, glue/acetone/cement may not be necessary to keep things together.
The front has support pieces built-in so the M3 bolt head is recessed; just snap them out.
Otherwise, construction is as per the instructions on makerbot's thingomatic PDF archive page.

Notes:

You may want to wait until the parts arrive to verify that all the bolt holes fit (especially the LCD).
The left-most (X-) button may be tight against the case front; you may need to shave a few microns off the left side of the hole.
Since plastic is a good source of static... be careful with the LCD -- there's warnings everywhere about static shock damage.

Case/Parts for Gen4 Interface Kit