Ok reading a bit more it seems hes swapping the engine ECU out for one from a wideband equipped car.
Bit tricky on a B5 though as you'd need to be on DBW, and only the immo3 equipped cars have the canbus guff that the later ECU's rely on.
You could convert to electronic pedal, but the immo would be tricky, and you'd need to find an entire engine harness from a suitable M7.5 car (B6 perhaps?) along with the throttle body etc.