I built something... similar. It was a load box, with an out for silent recording, rather than an attenuator but the core is basically the same (I've been meaning to write it up for the forum... maybe this is a good kickstart). @klaasvakie helped with the inductor calcs and sourcing the components. I know he was looking at this circuit but I'm not sure how far he is.
The biggest trick is winding the inductors, which I found very intimidating but turned out to be relatively easy. Honestly, once you have those, the resistors and switches are simple.
I'm not planning on building one myself any time soon I'm afraid, but for someone of your skill I doubt it would be more than an afternoon's work, especially if you simplify the design.