gunk under intake manifold

Unless you are removing the engine, here is what I would do.

Jack the engine up and remove the oil pan. Remove the valve covers, as the sludge will be in the heads, too. Loosen it up with a gasket scraper. Then get a wet or dry vac and vacuum as much out as possible.

Next, get some purple power and a squirt bottle. Squirt the intake valley and heads down with 100% purple power and let it sit about 30 minutes. Fire up your pressure washer and pressure wash the inside of the intake valley and heads. It's nasty, but it works very well. I have done many like this. Works real good.

Of course all this is unnecessary if you decide to remove the engine.