There should be a sticker on the inside of the breaker panel, backside of the door, etc. that states the manufacturer's breaker styles that the panel will accept. Get that style in a 50A/230V breaker.

You left out the most important pic: the front of the breaker. The style of breaker should be printed on the face. Square D makes several styles of panels and associated breakers.

The front of the breaker just has the Amerperage rating on it. The panel itself looks like it has several coats of paint on it.

The sticker with the breaker style should be on the inside of the panel.

The paint obscures most of it with only the pen markings and some faded print that are left outside of the painted area. The Square D imprint is hard to read on the panel itself due to all the paint. I had to clean some paint off the breaker shown above as well.

Then you'll have to take the old breaker and physically match it up with the new breaker.

Thanks! I did that yesterday and one pole is dead! I went from 180V to 73V. ☹

Sounds like the issue isn't the breaker!

Yes, I agree with that thought. At this point, I'm beginning to think it is wiring related.

The box is really old and the previous owners doubled most of the breakers during their remodel.