Second, NKP 6000-6599, 600 PS-1 cars, built 1948. I need to know:
1) What kind of roofwalk were they built with?

Apex Tri-Lok.

2) What kind of handbrake were they built with?

Ajax.

3) What is the build date (one photo looks like 2-48)?

The NKP diagram sheet says 2/1948.

4) Were they delivered with black roofs or ends?

It doesn't appear so. The only photos I have of these cars new is of 6816
(built later in 1948) and that car has BCR ends and roof.

Hope this helps. I've got 12 photos of NKP PS-1s. Let me know if you need
any emailed to ya.

Ray Breyer