Quantity   Component name
1 × Psion Organiser II I'm using the 32K XP model (sometimes also called the LA) introduced in 1987. There was a cheaper model with 8K RAM called the CM, and a 'deluxe' model called the LZ which was introduced in 1989 and had a 4-line display. Ooh, fancy!
1 × Psion Comms Link A remarkably hard-to-find Organiser peripheral. Vintage units from the 80s have an RS232 port, modern units have a USB.
1 × Raspberry Pi Pretty much any model will do, though for added elegance you might want to pick one of the newer ones with WiFi.
1 × RS232-to-TTL converter (+ maybe a serial adaptor) To convert Ye Olde RS232 signals to modern flashy TTL signals, and back again.