A radiator pressure tester should tell you if you have a coolant leak. A combustion leak detector will tell you if the head gasket is leaking combustion gas into the coolant. Both testers are not that expensive.
The head is not difficult to remove and replace with the engine in the car. However, I would not recommend replacing the water pump without removing the engine.
So, maybe remove the head and see how the cylinders and pistons look. If not good, you can still go ahead and remove the engine and transaxle. It's just lighter.
Btw, nice looking car.