I hurriedly made up some components so I could see what was involved in hanging test indicators off the mill head.
This attempt shows the assembly mounted to the quill depth stop.
I've used this assembly a lot and it is turning out to be quite convenient and I can set up a test indicator in well under a minute.
I plan to install an M8 thread in the end of the mill quill nose plate. I can then mount the dti assembly to that, and move the test indicators up and down using the quill fine feed.
Here are the crude components and assembly.
The black clamp is off the magnetic dti set, and I added an old brass wingnut.
I found the piece of aluminium rod in the scrap box, and will replace it when I get a round tuit.