If you go 3 gear MM then you dont need to buy anything. The chassis brace and wing mount needed are in the parts tree bag that you get with the RTR. I went with 4 gear.
For MM4, you need another Idle gear and Idle shaft and Idle shaft washers and bearings. Part numbers can be found on this page:
http://www.team-durango.com/race-cars/dex210rtr/
Everything explained in here:
http://www.team-durango.com/blog/201...onfigurations/