What's under this plate?

I remember cleaning out that passage and the holes in the heads that were plugged with carbon on my '69 Coronet 318.
I used a chisel to turn the screws out, it was pretty easy.
After the heat crossover was cleaned out, the choke and carb worked way better when the engine was cold, the stumble disappeared entirely which made the car much better to drive especially when it was -30 below F.
You'll be happy that you did.........