I received quite a few switches and more will come later !

These are 10 interlocked switches, with their caps, and they are just like I wanted :-)

2 of them will be used for the opcode selector.

For the other selectors I needed somethign more simple and pre-made, and I have found it in the form of the 8-channels video selectors. And I have a good surprise ! Look:

I expected the box to contain a single PCB but there are two, making the switches assembly very easy to remove !

2 screws and 2 connectors to remove, and there you have the module :-)

The traces are easy to follow and they are already conveniently wired for my purpose :

The SRI, SND and CND fields are 3 bits wide, and the selector outputs 3 bits, which is a great match.

I can wire the switches' inputs to a common rail, such that the 3 output bits will contain the binary code of the selected button. I can also bind the boards together to make a more sturdy structure (I have 2 but need a 3rd for the conditions).

There is a last technical problem though, with the hexadecimal encoder : the lower nibble requires a type of switch I don't own... But @Artem Kashkanov has the perfect part ! From Russia, of course ;-)

This selector has individual SPDT switches for each bit, making my diodes hack possible :-)

I'm still missing a few extra switches but they'll come soon enough.

At least I successfully designed a fully-passive assembler panel, with only one diode drop on certain signals, and no requirement of external power (no relay or other logic). The panel can work with relay logic, transistors, TTL...

Time to think about the disassembler panel now ;-)

I can say it works very nicely :-)

I'm waiting for the delivery of the 3rd module so I can have all the necessary buttons for the SND, SRI and CND fields.