I have for sale an RBR suspension upgrade with chin cup as sold by Brigade Quartermasters, among others. It has been opened and I installed it, but never used it or the helmet that I installed it on.
The only thing that has been done to this was a small 3/4" hole that I cut in the skull pad for comfort (it's a round piece of gray foam rubber).
You get over a $20 discount for an opened kit. SOLD