Rust in Intake Port??

Naval jelly. Easy to apply, easy to remove, acts quick. Oil heavily after with wd40, 3 in one, motor oil or similar. I like gear oil because that stuff sticks to everything but it stinks.

Muriatic acid will fume and rust everything in the room, unless you're far more careful than I was/am. It will even eat chrome off your tools... Expensive lesson (I etched some floorboard with 1/2 cup of muriatic and stored the well sealed bottle in the garage with the car and tools.. Wasn't well sealesd enough).

Pressure washing is fine, but drying the whole head before rust forms can be tough, and it may not remove everything.

Vinegar is great, but trying to plug everything and isolate just the port will be a pain in the aft end, and it won't touch anything that has any oil or other occluding agents present (even fingerprints can slow the vinegars action). If left long enough, it will get through light oil but will also etch more off of surrounding surfaces. If you're gonna soak the whole head, no cheaper or more effective method though.

After the port is clean, make sure the valve guide and valve stem are good and not etched or pitted by the rust prior to reassembly.