The Osborne keyboard doesn't contain any electronics, so the pins of the 8x8 keyboard matrix are easily available right on the normal connector. 17 jumper wires and a Feather BlueFruit is all the additional hardware needed.
Make example for this keyboard (after setting up your build environment):
make osborne1:default
Flashing example for this keyboard:
make osborne1:default:flash
See the build environment setup and the make instructions for more information. Brand new to QMK? Start with our Complete Newbs Guide.
Enter the bootloader: