Water Jacket Help needed

[Diastole]

Water Jacket Rust Scale

I am in the process of changing my head gasket and head to a 5.5 compression variant.

Reason: leaking head gasket (likely from weakened and galled studs) and engine eating water.

Everything looks good, cylinders’s ridge almost in-perceivable, valves clean and seat well, block's deck's flatness (0.002”), no cracks, no issues my club’s advisors can see except …

The problem is, peering into the water jacket, there is a moderate amount of rust and rust scale. See photos

What do I do?
Now is the best time to do something big.

Thinking through my options:
1. Pipe brushes, solvent, and elbow grease
2. EvapoRust (I have one gallon of the liquid, but not familiar with its use)
3. Metal stripping acid like phosphoric acid

The engine is in the car still.

The little bit of copper (it is not rust) on the engine deck is after test fitting the 509C gasket with the copper spray.

Thanks, in advance, for all the advice and guidance.

Diastole in the Smoky Mountains