Copy the canceled check number and the names on the letters before you do ANYTHING, that's your paper trail. The $12,000 check probably had a bank or attorney's name on it, and you can call that place to see if they can point you toward the family. Post the letters if you want, but blur out the names and addresses, that's the classy move.

That edge finder has ears and eyes that no probe will ever match. I did the same thing with a digital height gauge a few years back, spent a fortune, and it still couldn't tell me when a burr was throwing off the reading the way my old mechanical one does. Plus, there's something honest about the wiggle and feel of a spring-loaded edge finder. You know it's right because you can hear it, not because some display says it's within a micron. Technology is great until it needs a firmware update to do what a piece of brass and a spring did for fifty years. These fancy tools are for the guys who don't trust their own hands anymore.