I'm wondering if the fixturing method used for non-crazy accuracy with two raw angle plate castings, using a lathe, might just work for crazy, as well?
Here's how:
On the lathe for non-crazy, you take one as-cast raw angle plate, flatten (not square) the faces with a file enough to mount it so it won't rock on the faceplate. It doesn't have to be square yet, just flat.
Then bolt it on to the faceplate with a shim under it until the extending face IS square to the faceplate, checking with a true square.
Then you take your second raw angle iron casting, flatten the faces as before, and mount it to the first angle iron leg, which you made square to the faceplate. It now has a raw face that is somewhat parallel with the faceplate, and you proceed to turn that off flat, which makes it truly parallel to the faceplate and square to the other leg of its angle plate.
Then you take apart the rig, and mount the newly squared angle plate to the faceplate, and mount the second (still untrued) faceplate to it, and face it's extended leg true. Now both angle plates are square (non-crazy).
A similar process may be possible fo you using a flat but not absolutely true angle plate (or even angle iron) with shim -- checked with your true square, to yield a vertical surface to your surface plate for mounting your second and important piece to be squared.