Upside down is probably fine. If you have the cover, there should be information on the inside of the door. If you don't you will be replacing the box anyway.
Is the disconnect fused? If so, what size fuses?
Here in CA, you couldn't just poke the wires through the knockouts, and need to secure the wires. Running wire in front of the 2x4 in an exposed location would be a problem.
But you live in TX with less burdensome regulation so maybe it is OK there?
I think you suspect that you will be replacing that box and you are probably right.