Whilst searching my compact Mac collection for the back case "bucket" off my Platinum Macintosh ED, I also came across the fact that I have a beige Macintosh 512k ED exactly the same as yours Jason. It's the only one I've got like it too.

I was under the impression there were 4 types/variations of Macintosh ED anyway, so would have to agree.

PS. I didn't find the back half of my Platinum Macintosh 512k-based ED (it remains just a front bezel)...