OS.18TZ tx is a very good motor for TNX. Too much power that is. The rotary carb that goes with it is a bit pain to tune. You can use the stock or cvrx slide carb, but you need this: http://www2.towerhobbies.com/cgi-bin...?&I=LXHKX2&P=7

You have to glue (CA) it onto the carb's neck and don't forget the black O-ring. No need to install BB because TZ is actually more powerful than OS.21rgxp. It is direct bolt in but you need a mods on the exhaust department.