I knew some day I'd find the smoking gun on this one and I just got lucky rifling through a stack of old Mainline Modeler magazines.
Mainline Modeler January 2002, page 40.
Black ends. No question.
The PRR cars were part of Lot 8160, all built with cushioned underframes, that was split up with BAR, C&O, Erie, GN, N&W, NYC and WP.
That January 2002 Mainline Modeler article with the PRR car photo is supposed to be about the entire Lot 8160.
Are there photos shown for cars from any of those other roads and, if so, are the ends obviously painted black?
If that's the case, one might presume the entire lot was painted similarly.