I think those would be too big
the mamba is a 280 size I think (but puts out 540 power almost)
I have seen others that are off set a little bit rather then inline
and I think if there is enough room one of those would fit better ( they also come in a range of gears)
I have put this project off for now (playing and fixing the RC18T) almost all aftermarket now)
Tell me how yours turns out when you start it
Nick