What parts to buy for MBXt6 M Spec

[wallot]

BCE chassis is not lighter, it is just more rigid which makes truck to be more stable during flight and in turns.

lightened drivetrain parts - aluminum axles and CVD joints from mugen

2x MUGE0242
1x MUGE0243

I recommend you to start with the stock truck and go from there. First you need to see how it handles. Some people prefer heavier truck as it is more stable.
My mugen is very aggressive with lots of grip that can be sometimes hard to control in turns as it likes to roll over thanks to all the grip.