Against my better judgement, I decided to mill the second face tonight. First, I used a marking gauge to scribe the target thickness into the edge of the board, then threw it rough-side-up on the bench:

Yeah. That’s about a quarter-inch that I had to knock off the board. That should sound like a pain. And it was. Sort of. It took a long time because I used only the #6, but I finally arrived at the goal:

This face turned out to be a little bit flatter than the first one. Practice, I guess. Or desperation. Whatever. It’s not as “smooth” as the first face, but that’s only because I decided that I didn’t want to get really anal with this, especially considering that a smoothing plane is going to hit it at some point.
If I have to do much more of this, I am seriously going to look into getting a scrub plane. The sheer number of shavings that I ended up with was ridiculous.
Next up, I’ll need to shoot one edge flat and square, rip to width, and plane the other edge. I probably need to improvise a shooting board for this.