There are potential for leaks, but it can and does work. You might find a commercial block off plate that is less likely to leak.
The arm on the pump is hitting the actuator cam and you are compressing the spring in the pump as you tighten the bolts down. Turn the engine half a turn or so and see if it gets easier. There are points in the engine's revolution where the arm is just barely compressed and places where it is highly compressed - which is where you probably are.