Yes the belgian built railways - it still operational - and still pretty much only means of transport plus airplanes. Otherwise to drive through Congo with a car - even 4WD - is pure madness.
They need to pour murram - at the very least.
Anyway if I was a president of DRC - I would mortage those minerals to chinese - in exchange for infrastructure.
I think Ghana just did that - gave Chinese bauxite - in exchange of infrastructure.
Just value the minerals - let chinese come with their armed forces - and they will pay DRC even 100B dollars - and begin road, power and rail constructions.
Chinese have transformed Angola and Zambia which are also huge messes.
Train would be better. Roads just do a museveni and use murram and stones to pave roads