What the heck is up with 8-3/4" rearends?

in 2004 I bought a drum to drum E body housing with a 741 2.94 obviously from a different car, not because I needed it, but because it was $100. I didn't even know it was E body then.

About 1.5 years ago, I bought another E body housing drum to drum but with the correct 489 case 2.76, again not because I needed it, but because it was $100.

For some reason I still see E body, and only E body housings for $100.
I believe some year C bodies use the same rear as the E bodies. The reason you are finding them cheap may be because they really came out of a C body.