Whoa! Don't leap to such conclusions just on my word. It could be cast iron, it could be steel, I don't know...it's a very minor detail that in the big picture doesn't mean much. All I know for sure is that it is not brass.

Rich, Les, and Kelly, thanks for your answers. In my honest opinion, I think this is the best the 765's ever looked (and sounded!), though pictures and video don't do it justice. Can't wait to see it at TrainFestival in July!

Well, I originally asked a question about the whistle issue, but I missed the post outlining the priming issues.
Anyway, here's proof that the whistle is the same.
2006 Break-in Run on the CF&E (similar to 1992 sound, slightly lower pitch): http://www.youtube.com/watch?v=PSQVohDemog
2009 Excursions on the CKIN (water issues): http://www.youtube.com/watch?v=GuZqU8fLOKs

The "C&0" style numberboard lettering raises an interesting question with me. For some reason I didn't think the S-2s were delivered with the numberboards, but they were added later. I remember seeing builders photos of the S-3s with the numberboards, from Lima, with the C&O style lettering. Did the NKP use the C&O style lettering on the numberboards it applied to the S-2s, before switching to the different style numbers? Or, did some of the S-2s come from the builder with those numberboards?

The NKP's S-2 Berkshires came in two batches. The first, 740-754, were delivered between January and March of 1944, and came without the flying numberboards. 755-769 were delivered in August and September 1944, and came with the flying numberboards and C&O-style font numerals.

This didn't last long. By 1945, all of the S-2 engines had flying numberboards and the traditional (and hand painted) NKP block numerals. So 765 is curently painted in her as-delivered scheme (after 1935 or so, the NKP repainted smoke and fireboxes gloss black, not graphite), which she likely wore for less than a full year.