Regarding the prices of 289s and 427s that year, I have several ads from 1975.
You sure this was 9/75 and not 9/76? I'm not doubting you, I'm only going from what I have in my ad library. $23k seems kinda high, there is one ad from that November though, I believe in the NYT, where a 427 that was asserted to be the "best in the world", was being offered for $22500 firm. At least in the first half of 75, and obviously there were a few exceptions, 427's were almost always in the $15k range.
CSX3350 was being offered, albeit in need of cosmetics but in "strong mechanical condition", for $13,000 in AWK 7/12/75.
Again, I'll upload some examples later today
