Technically just the motor, ESC and plugs.
After that it'll be what ever breaks. And other parts will start to fade or fail eventually with the extra power. As an FYI......with the MLST being one of the bigger and heaveir micro's, the motors that offer more torque than speed usealy perform better in it.
Make sure the gears are nice and tight and everything else is in good running order. Read thru some of the diff arrengments, this will be a good place to invest in. BUT, none of them are fool proof still !

Some CVD's are also good parts.
Whenever anyone upgrades to a BL motor, they don't always think to upgrade their radio. But a good, reliabvle radio and Rx are essential whenever that much speed and power are involved.