Starting at 12.20 is the big struggle with a 4100.
I forget how I removed the palnut but it was either a miniature cutoff wheel or a pair of tiny needle nose pliers and pointy wire cutters.
I left the palnut off and assembled the secondary circuit to confirm that the butterflies would open and hold on a vacuum pull since the slightest air leak or passage restriction would render the circuit weak and ineffective, your 4 barrel fun just went out the window!
Oh yes, and be darn sure the secondary diaphragm is oriented correctly before you push the new palnut into position and have to remove it, ask me how I know.