Are you talking about midifying a Rodgers Trio 321B/C?
The pedals switch 12 Volts and do not carry sound signals, that makes it easy.
If you just want to use the pedals as a controller, wire each pedal to a diode, then a voltage divider to break down the signal to max 5V and connect them to the ports of a Teensy 3.5, which if the only powerful Teensy with 5V tolerance, or break down the signal to max 3.3V and use a Teeny 3.6. They have plenty of power and plenty of pins (57 on the Teensy 3.6).
The rest is simple Arduino.
If you want to play the Rodgers with MIDI, then you'd need high side switches to send the 12V signal to the key contacts, or better to the input resistors of the keyer diodes. 32 pins of the Teensy to drive high side switches, plus input 2x 74hc4067 input multiplexers to scan for keypresses, wired like above.
But you wrote, you've done this several times so?