I was talking to my neighbor about it and he gave me a contact to a mobile welder he knows. Basically a similar plan is what we came up with. Weld a steel plate to the top and bottom of the 8x8 door with holes drilled in them.
We couldn’t figure out a method to cover the holes though.
Do you mean something that would look like this?
We couldn’t figure out a method to cover the holes though.
Do you mean something that would look like this?

I used a 55 gallon stove door I was able to find laying about. I'd get a cheaper wire feed welder and make you something up. What Dave showed you can be made with simple cold rolled steel or what ever you can scrounge.
Don't go too cheap on a welder, because, once you make one thing the ideas are going to flow for other projects. You buy that welder, you might as well buy an angle grinder. They go hand in hand with metal working.
How about closing your opening with another brick and using the 8x8 door. Drill a hole and larger plate with a hole that can cover it and a lock washer to bolt it on under tension. A handle on the plate and slide it to adjust the holes ability to draft air.