I recently added basic SPI support to my 80286 system with the help of a W65C22S Versatile Interface Adapter (VIA).
Additional Reading About SPI
I am currently using a programmable system-on-chip (PSoC) from Cypress to handle address decoding. Below is the current configuration of the PSoC.
The following schematic is as of 23 November 2022.
This assembly I used during this video is available on my GitHub: Assembly Used in Video.