gunk under intake manifold

So I’ve been working on my 318 and first I saw the thermostat housing had a lot of what looks like old rust caked in it. So I under advice to check out what’s going on under the intake manifold I just removed the intake. Im new to this all, I know the engines 40+years old and sat for who knows how long but this seems pretty bad to me. Opinions? Options on cleaning the gunk? Anything lol