What you have is no different from what we all see when servicing engine cooling systems that have not been maintained over the last 30+ years. What else would you expect?
All that matters is that the system is properly serviced now.
And that includes an entire cooling system chemical flush (several times if needed), replacement of all hoses, complete service of the radiator for both flow and pressurization, replacement of the thermostat with a proper rs370-pattern unit, replacement of the water pump if any leakage indication is seen around the vent hole underneath the shaft boss. A new 13lb. Pressure cap should also be installed and the radiator plumbed into a proper burp bottle (coolant recovery system) similar to the oem design.
If ya don't replace the water pump now, when all the above is performed and completed, you most likely will find that the water pump leaks after the chemical flush is performed. Same for one or more of the soft plugs in the block/heads.
Once the entire cooling system is re-installed and connected, it should be filled with straight water (no antifreeze) and then air burped and the system pressure tested. If it won't hold pressure, then you have a leak(s) and the engine is going to overheat. If the cooling system passes a pressure test and will hold pressure (not leak down), then drain and fill with a proper 50/50 mix of antifreeze (do not use anything that refers to dex-cool!!!). At that point, the system will have to be air burped one last time...all entrained air must be removed from the cooling system and that require patience.
All the above is referred to as "maintenance" which has long been deferred in the case of the subject vehicle.
