mudguards - yes, however :)
first and last hole is direct fit. you will have to redrill two midlle ones and use lock nut to secure the mud guard.
http://img.rcx.cz/nm2.jpg
i use mbx6 mud guards on my mugen as they are much taller in front
arms. they should however it I would go for complete (lower/upper arm) swap as the geometry is different.
also at least on mbx6 buggy the arm material is different from mbx5 and does break more easily.