I needed to drill far fewer holes in OOSOBO than on some rebuilds, so there was that.
I was installing the foot brace from vague memory, but you surmise correctly, I wanted the big goobered end of the pop rivet, aka the rivet pin and mandrel head, out of sight, both for aesthetic reasons and because they can be scratchy sharp. I had rounded all of the edges and corners on the L bracket so there were no sharp edges exposed.
I move the bar to different holes after it was installed and it was easier to have the wing nut on top and the machine screw thread sticking up where I could see what I was doing.
Unscrewing the wing nut I held it in one hand and held the machine screw (and lock washer), still through the foot brace bar, with a finger, poked it up through the desired hole and threaded the wing nut. That adjustment seemed easier than dealing with loose pieces of hardware at each end of the bar.
I don’t know if there are structural issues with the bar and brackets mounted one way or the other. I should probably adopt Glenn’s foot brace hardware strategy and put spare machine screws, wing nuts and lock washers inside the foot brace bar.