Up down window balancer

Looks like the window manufacturer used a horizontal sliding window roller assembly. They removed the wheel and used the nylon housing. We have a black top sash guide, the 18-008, that doesn't have a top cap, but I believe it should work. 

For the channel balance, you either have S351-28 or S390-28, depending on the depth of the bottom nylon shoe. The stamp option in either case will be 2730.