Enjoyed reading your build Daniel, it's going to be a beast!
As far as the speedometer issue, it might be worth trying a new sensor. I removed the "sensor wheel" on my old Birkin and just aimed the sensor at the bolt heads on the driveshaft with the correct gap and it always worked perfectly for me. If you're not able to get it to work there are always GPS speedometers that I've heard work well but have no personal experience. Speedhut even has gauges that you can change the looks of (font, needle color, etc) to try to match your original gauges.