Don't buy the stronger 31.45% solution of Muratic Acid (31.45% Hydrochloric Acid) and mess with it straight. I just went through that ordeal. It's nasty and chokes you out just pouring it out of the bottle.

Get the 15% "low odor" stuff.

It does flash rust uber fast. I dunked it in straight water immediately and directly to neutralize it. While gagging from momentarily opening and closing the ice chest with 3 gallons of 30% Muratic Acid.

After dunking it while still wet I sprayed rust Justice Brother Chain Lube oil (thicker consistency with rust preventative). Kept spraying it to displace the water.

Day later I rubbed off the excess oil.

The manifold on top I just brushed on straight 30% muratic acid with a steel brush and washed with water.

IMHO, I have seen NOS manifolds look like both of them. One on top if the packing oil has evaporated/worn off of it.

BTW these were very nice So Cal manifolds that were recently on a car. No pitting to start with. The heat riser weight was not submerged in the solution as it was just above the Muriatic Acid level.