Foundation vent mesh, trim, fasteners, paint.

Yes, those covers were probably put on in the 60's when the house was last updated. If I were to make my own, what mesh material and thickness would I need? Can I just do a simple wood frame around a piece of mesh metal?

The frame should be metal, and should have a damper in it to close the metal plate behind it. It might be a good idea for you to go to the Big Box store, and take a look at real metal foundation vents, so you have an idea how they are supposed to look, before you decide to make them.

@cat_ky
Thank you for the suggestion. I assumed it was a simple metal mesh with a wooden frame but there's probably a lot more to it. I'll check them out 🙂

The mesh you're looking for is called 'hardware cloth' - at your local hardware store.