Well my port extender hat finally arrived so I got busy wiring the front panel to the Raspberry Pi via the extender.
The port extender came with standoffs, so I used two diagonal corner holes on the Raspberry Pi to mount it to the bottom frame, and the opposite two corner holes with the standoffs to support the hat. Seems reasonably solid.
In the following photo I'm about half done. A ground wire has been routed to all of the front panel components, the fifteen push buttons have been connected to the hat, and the twelve LEDs have a short wire with a limiting resistor attached. The resistors are 10k to keep the brightness down.
I used female headers to connect the front panel lights and buttons to the extender. Because there wasn't a lot of head room with the top frame on, and space between the male headers on the board, I had to angle the wires as in the photo below.
It was a little tight, and as I soldered the wires onto the the header I kept asking myself why I hadn't designed a PCB for the front panel. At the end of the day though it worked out OK.
The red heat shrink protects the "inline" limiting resistors for the LEDs. A few cable ties and my KENBAK-2/5 is ready to go.
Next step is to write the code to manage the front panel and integrate it with my Emulator.