Jean-Claude
Great idea, drill from the bottom, sight from the top.
I'm having a bizarre idea this morning. There are lots of 1950s jig saws like http://www.vintagemachinery.org/photoindex/detail.aspx?id=10644 available for cheap. The platform could be converted into your type of drill by raising the table a few inches and mounting the drill motor on the lower chuck. Attach a lever to the drive pulley and install a USB microscope in the spring tower.
There is an exploded drawing in Sears | Craftsman - Publication Reprints - 103.20720 Craftsman 18-inch Jig Saw | VintageMachinery.org