On my 74 318, I removed the manifold and chiseled out the carbon with drift punches and a screwdriver. After the first layer or two, the stuff was a lot softer. Thought it was caked with anthracite. I tried to disconnect the EGR stuff but an emissions inspector spotted the modification and flunked me so I had to clean it out.
As a firefighter I love and loathe the torch trick. I would have done that myself if I had thought of it but I can see a smoldering garage in my future if I try that.
Craig