In 90's I did something similar (hardware wise), only not with bus, but with central "hub" consisting of matrix of diodes (arranged such that each station would

In 90's I did something similar (hardware wise), only not with bus, but with central "hub" consisting of matrix of diodes (arranged such that each station would send data to each other, but not back to itself). As for framing I used two upper bits of byte as overhead and only transferred six bits per physical 10bit UART frame (original inspiration was 8051's "9-bit networking").