Sorry I didn't want to remove the dust from this topic, but I've got a few questions regarding your mod.
I was planning on doing almost the same thing as you, and today I finally found out that I wasn't the only one who had this in mind.
Now for the questions, how did you connect the wires from the 56k to the line simulator? Do you have any schematics drawn at that time, if so do you mind sharing them?
Cool project and I'm glad I'm not the first to this project
Edit, when the parts arrive later this week like the Pico Psu, raspberry pi zero w, 56k usb modem and a 5v to 9v converter, I would love to document the process for you guys