I've cleaned an Olds 350 many years ago where the intake valley was slam FULL of that mess. On that particular job, I removed the oil pan. When I got all of it out of the intake valley and heads, I taped off the intake ports with duct tape and used a pressure washer and blasted the intake valley and inside of the heads after I let some purple stuff sit in it till the next day. It came VERY clean. Because of the sludge stopping up some of the pushrods, it burned up several of the aluminum rocker arm hold downs and the valve train was very noisy and the engine ran terribly. I also ended up putting a new oil pump and pickup on it, as well as a new timing chain set. When I got done that was one of the smoothest running Olds engine I've ever seen. It was crying for help.