I drained and refilled and managed to get it with no air trapped by going painfully slow. Like, pour a cup in the expansion tank, pour a cup through the upper radiator hose, wait 5-10 minutes, and do it again.

The thermostat only fits one direction. I'm not sure which way the valve is oriented, though.

Unfortunately, I'm still having flow problems (temps are back to about what they were before I did the work), so it looks like I need to replace my radiator after all. Darn, I was trying to avoid that.