why can't you Z the rear too?

[63 & 64 Bowties]

This is probably a dumb question because I've never done a Z or a notch. But, I'll probably attempt something on my 66 longbed soon.
But I was wondering why I've never seen anyone Z the rear frame just like's done on the front. Looking at the rear, it looks like you could just cut the frame about 10 or 12 inches behind the cab (before the trailing arms pass back under the frame) then just change the pinion angle and bag it using the stock trailing arms. I didn't take measurements, but it looks like it would give you about 6 or 8 inches of drop since the frame is pretty wide there, then with bags on the stock suspension, it may not lay frame, but it should be pretty close.
I started out by saying this is a dumb question, so what am I missing? I'm sure there's something or someone would have already done it.
thanks