Stick with plan C
I would recommend plan C!
Kinshasa too many corrupt officials and too much money for ferry.
Just came back from Louzi(month ago)crossing,motorbike is free and they
Will help you to load your bike on ferry for free.
In Kishasa,3 weeks ago they charge(Filip on Ktm from S,Africa)$40usd JUST to load and $40usd to unload +big money for ferry ticket+ port fee this port fee that,CRAZY!
If you going from Congo Brazza to DRC they charge me 1000CFA=$1.80USD.
@530cfa per $1.
And if you in brazzaville, stop by @hippocampe the ovelanders camp for free!
The only negative side some sectons of the road from Louzi to Boko are in rough shape!
I would not recommend in rain season!