I can assure you that they are NOT. They began to show up on (mostly) GM stuff around 65?6? and were used up until EFI was used. They were used on literally every V8 that GM produced, so Caddy, Olds, Blueuck, Chiv, GMC, etc etc etc, and between the several brands and large model exposure, and the long run in years, these were installed and operated for zillions of miles on millions and millions of cars and trucks.
The one(s) I ran on my 340 ran very very well. Part of the reason I ran these is that I could "get cores" because back then TQs were having warpage and leakage problems with the main bodies, and I could not get many cores.