Nick,
I think that "The Great Whistle Storm" was a contrived event, just as the lack of a "Canteen" that Link asked to be removed between the lead and second engine in order for him to get both locos in the same frame. I also don't think that there were any road crossings near the top of the Blue Ridge grade, although there were some overhead bridges in the area. One bridge in particular was near the top of the grade and known as "Photographer's Bridge". I think that this area was where Link and others did a lot of recording. The bridge is now gone, but you can still get to where it had been.
The Bud Swearer tapes specifically note that whistling was asked for during the time of his recordings. A lot of engineers would comply, but, others did not, leading me to believe that there was no road crossing in the immediate area.
I would like to see the topo maps of that time. Do you have a link to it?
I don't doubt that "The Great Whistle Storm" was performed at Mr. Link's request, but the excerpts of whistling in the distance were probably legit. I only threw in the reference to "The Great Whistle Storm" to describe the incredible sounds, not to suggest that it was a crossing signal.
There was, as you say, the "photographer's bridge" to the west of the Blue Ridge Depot. The actual summit is in the cut between he station and the old west end of the Villamont center siding (where the pushers cut off on the fly). I believe Link was set up near the Stepping Stone Rd. bridge, behind the present day Boxley Concrete Products facility, which was just west of the switches for the center siding. The main tracks have never been re-aligned, spreading out at that point, so it's quite easy to identify where the siding began.
I've experienced the 1218's whistle on a number of occasions. It can be heard at an amazing distance, even with the ambient noise in the daytime. At night, with refraction of sound waves caused by temperature inversion, and with the absence of daytime noise interference, it should be possible to hear that whistle for a number of miles, especially in that mountainous terrain.
Link had the gain cranked way up on those short sequences, as evidenced by the sounds of the crickets. As the train drew closer, he lowered the gain and the cricket noises became less prominent, relative to the whistling.
You can view topos and aerials on https://www.historicaerials.com/viewer. It's a great resource.