intake port plugged

I started pulling apart a spare 360 I have laying around. I am planning on putting it in my 72 swinger until I get my other motor rebuilt. I was told this engine ran well, 73 360, 110k miles on it. I pulled the the 2 barrel intake off to put on a performer and holley 600. When I removed it I notice the middle port is plugged on intake and head with hard black carbon. I believe it is for heat transfer but I am not sure. I did not have a camera with so I don't have a picture, it is the middle port with a half moon above it.What is the best way to clean this without damaging engine and getting carbon everywhere? I scratched at it with screwdriver and it is like a rock. Would it hurt to leave it?