KAWADA released two option parts for their M300.
1) SSG chassis
http://www.pro-s-futaba.co.jp/kawada_rsw1s.jpg
2) Delrin friction plate
http://www.pro-s-futaba.co.jp/kawada_rs771.jpg
Shooter released many option parts for RC12L3
3) See following japanese page you can see pics.
http://www.hirofactory.jp/develop/heros/s_L-parts1.htm