TDP, your series mark looks more like a 22 than a 20 to me. Also, Monopods and Action Dust Covers (both original and aftermarket) are available. Not a bad looking 99 though... and with a full mum to boot!

My Toyo Kogyo Series 31 has the mum, along with the Dust Cover, Monopod, Chrome Bore, Anti-Aircraft sight, etc. The only thing I'm missing is the sling. My Nagoya Series 7 is ground and sporterized into a hunting rifle... but still shoots awesome!