mesa 5i20 + 7i44 +7i73

What sort of switches are the two on the right top of the panel?

jtc wrote:

they are position switches from the old machine. I already reverse engineered one (truth table).

You can probably use "weighted_sum" to decode them:
www.linuxcnc.org/docs/html/man/man9/weighted_sum.9.html

The 7i73 is a complicated little beast, depending on the jumper positions and the selected software mode it can operate in 18 different modes.
I think you want software mode 0, though.
You have a lot of switches there, you might not have enough individual input pins on the 7i73 to have one-pin-per switch. That might mean that it makes sense to wire the switches in a matrix. Don't wire any non-momentary switches that way, though, as matrix wiring only supports 2 buttons being "on" at a time. If you do wire that way, you will need:
www.linuxcnc.org/docs/devel/html/man/man9/matrix_kb.9.html
Which only exists in the development version. (But can, I think, be added to an installed system)
I think what I am saying is, count your switches carefully.

emcPT wrote:

We have 27 inputs on that panel + encoder. I think that we can use at most 24 inputs on the 7i73, but as we also have a 7i37 we will manage it.

I think it might make sense to set up the 7i73 in 4x4 matrix mode for the momentary buttons. That gives you 16 buttons on 4 input pins (and uses 4 output pins too, but you probably have enough of those)