Well that is not absolutly conclusive but the head gasket is probably not breeched at the oil passage near the number one cylinder. Good going.

Next check for evidence of a steady stream of bubbles in the cooling system after filling it. Watch the surface with the coolant cap off.Leave the coolant cap off from the time of cold engine start. To try to remove the cap after the coolant has gotten hot could be a safety issue.

Even with the coolant cold it might try to blow it out the fill point with your type of indicated problem. People have gotten badly scalded even with a normal engine by removal of the cap while the coolant was hot.

If either of those symptoms are present there are problems with the head or head gasket. I also can think of no reason this car engine would not respond simularily to the 603. Your engine is basically the same with one less cylinder.

Start the car with the coolant system sealed up. Warm the engine to the normal running temperature. Check the hoses for hardness. Shut the engine down.

If the rad hoses are still hard the next morning this indicates a cracked head more than a head gasket. You should be making some progress with these tests. Mention any observations on this site.

Many will be watching to help out. Some of your symptoms are actually good. They indicate the lower block may still be fine with any trouble still confined to the upper portion of the engine at this point. As you follow through on and post on each test. Many members smarter than me will chime in to help as well.

Actually you may have already answered the question earlier. If the engine was cold when you took off the cap and coolant or air expelled rapidly all you will be doing now is isolating the problem to either the head or head gasket before taking the head off.

As a general practice I never take an engine apart until I have established as much as possible what is actually wrong. I work at it until I am certain of where the problem is exactly inside. All kinds of simple tests are engineered as I go along if the easy universal ones do not answer my questions.

Once the basic tests are over we can find out a lot more yet. I have to do this as I am not a working mechanic. That means no instinctive or intuitive knowledge from a lot of day to day experience.