Today my plan is to:

Pull the plugs and have a look at them.
Do a compression check with out any coolant in the system.
Reinstall timing cover and water pump.

If a plug looks clean and the pressure in that cylinder is low I'll just start pulling the motor. This will be to address the freeze plugs and possible head gasket.

If the plugs look good (dirty) and cylinder pressure all check ok. I'll finish installing the coolant system and then do a pressure check.

Next I'll go after the catalytic converter and monitor the freeze plugs.

Fingers crossed some something shows the correct path to repair.