Here is a tool I built a few years ago when we were doing a lot of work with the Mill at the shop. Pretty simple contraption, really. ...just a few odds and ends from the scrap pile, a couple of HF dial indicators and a few set screws.
I cleaned up the stainless shaft, drilled a few holes in the aluminum rod, drilled and tapped a couple of holes for set screws. I also tried to whipped up a jig for letter stamping, but didn't have the best luck (if you look closely, you can see a little double striking). I then chamfered the edges, hit the whole thing with a little scotch brite, and then threw it all together.
Now, whenever I have to square things up, I have a tool to do it. ...And all it took was a little effort on an otherwise uneventful Saturday afternoon.
These have been done before, so it's not like it's anything all that new. Dale from Metal Tips and Tricks did a great video on building and using one of these, that would be a great resource for anyone interested in making one of their own.