While I'm waiting to continue work on the keyboard, I may as well start thinking about how to lay out the internals.
Obviously the Raspberry Pi 4 will take center stage, but it will have to share the case with all the support electronics: LCD driver, USB hub, SSD, keyboard controller, touchpad, and battery/charge controller. There will probably be more, especially if I can fit those parts in efficiently. To that end, I will probably roll my own support board with a USB hub IC, Teensy, and the necessary cable connectors. I'll have to decide if I want to keep the old floppy drive bay covered, or cut that portion out of the support frame.
Because literally none of the external ports on the Powerbook 190 are still in use, with the exception of the barrel connector for power, I'll have to be creative fitting the Pi's connections into the existing holes. It'll probably end up looking like an octopus, with extension cables running to different places on the case. One USB 2.0 port will be reserved for connection to the input devices through the hub, and one USB 3.0 port will be connected to an SSD. Only one of each will be broken out as external connections, along with Ethernet and one HDMI port. I think a 3D printed cover plate will be called for here. Given the concave shape of the port area, a cover place could probably fit right on the outside and only expose the modern ports. This would remove a little of the retro appeal, but give it a much cleaner look.
As you can see, repairs on the case and removal of the battery leakage are ongoing, but it's getting there.