I prepared the front and rear stretchers in the frame for the square holes. What this means is that I cut the hole outline with a knife into the wood, then pare to that line with a chisel. This process is repeated several times for both sides of each hole, because this wood is more prone to tearout than a typical hardwood.
When ready to start drilling the holes, it looks like this:

The hole is on the right side of the board here. When I’m ready to start again, I drill four holes through to the other side in each corner of the rectangle, then put a coping saw blade through one and saw around. Here’s a close-up of the other end (ignore that circle in the center of the hole; I was playing around with one of my new brad-point bits):

The board is a 2×8. The tree that this board came from is a little different than the one that the 2x4s came from. There is a lot more latewood in this guy, making it quite a bit more difficult to slice through. However, it is also nice and heavy.
That try square is an item that I found in the toolkit at my mom’s place in October. It was made by Stanley, and had a lot more rust on it until Thursday, when I decided that I’d had enough of not being able to see the markings and numbers on there. I just did the usual mineral spirits / sandpaper / wax treatment that you’d do to a handsaw.
I don’t know the origin of the square. It has BPS15 stamped into the handle, which probably means Baltimore Public Schools 15. That wouldn’t be the current BPS15. I asked my mom about that today; she doesn’t recall anything about it, and speculated that it may have belonged to my grandfather (my father’s father, that is).
Also, a much-anticipated package from Lee Valley Tools arrived today with my brad-point bits, my “Wonder Dog,” and perhaps most importantly, my auger bit file (couldn’t find one anywhere around here, of course…). Naturally, I had to see if I could get my 3/8″ auger bit into some sort of more useful shape. That bit is definitely one of those “sheesh, quality control these days” cases, but with a little work, the cutting edges actually look like cutting edges, rather than sofas. I tried it out and it seems to work… but the real test comes when I start to put the fastener holes in the stretchers.