If I remember right, it needs to be flexed out an inch or so. It was slightly more than I could do with my hands, so I used a breaker bar inserted into the front opening of the coolant pipe. That gave me the leverage to flex it just enough to get the valve cover off and back on again.

This was with the coolant pipe side bolt removed and the rear bolt still installed.

Later, when I had the engine out for my six speed conversion, I removed the coolant pipe completely to replace the seals. Having done that with the engine out, I’m glad I didn’t fully remove it to remove the valve covers. It would be very difficult to reinstall with the engine still in the car.