well, of course, as soon as I post the question, I stumble across a bit of an answer in a different search and also in my own crap pile of brochures. The latter confirmed dark red carpet would have been installed, and the thread of MrDanB's 77 (the year Bonanza I was really looking at this for) showed some good ref pics (below).
Bonanza RPO question - I thought the YG6/7/8 RPO was always shown for Bonanzas (like in the 3rd pic of a different 77 Bonanza)? MrDanB's didn't show that but all indications were that it was a Bonanza - here's his thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=662391