Continuity Testing Between Two Inputs (Keyboard Matrix Decoder)

Hey there! I got my hands on a Data General Keyboard and wanted to make it usable as my daily driver through USB, but I've run into a problem...

Due to the keyboard having a strange I/O, baud rate, and command keys that wouldn't register as labelled on modern PC's, I want to take the output directly from the key matrix (it uses the membrane method) and use that as an input to the Arduino, then send commands from the Arduino to the computer.

I planned on using the SN74HC165N chip to extend the amount of inputs, but I'm not sure how to actually test whether a key has been pressed.

I'm wondering if there is a way to test continuity between two inputs. I know about the I/O scanning method where you turn each input into an output but since I'd have to cycle through 20 outputs I was worried that would cycle too slow for typing.

I'm also wondering if I'm going about this the wrong way since I will be using the chip above to transfer serial data to the Arduino for the inputs.

Any insight will be greatly appreciated.

Don't know if it's useful but, you could configure a MPC23017 as up to sixteen inputs and configure its interrupt to signal the Arduino when a key press is detected.