Hi,
I have 2 of this HPC, one is working fine, the other is really damaged, dead pcmcia port, dead screen flex cable, no battery, ideal candidate for something like this.
The main issues right now is to make the keyboard work as a usb device and make the screen works or found a decent alternative that can fit in the space.
I've seen someone do the same with a trs 80 handheld. He hooked the keyboard up to the gpio pins can we do the same with the nec 750c? I would love to put a pi 4 in mine. I don't belive his was a pi it was another mobo like the pi.