The washers are good insurance, regardless of whether they are factory spec for whatever year you have, or not. The key is to make sure the contact surface between the screw head and moon plate are clean & dry. After installing and test-driving it's always a good idea to check for tightness again. The M8 CV screws are known to come loose.
The M10 like Tippy has rarely come loose. I've tracked my '87 for years and every time I check the M10 screws, not one is ever loose. Not even slightly. However on my '79 racecar, every once in a while i'll see the paint safety marks slightly misaligned. It's a good way to watch your screws w/out having to torque check them all.
This season the '79 gets a new supply of screws with moon plates and serrated washers.
BTW the bell crank is part number 911.423.017.01
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW
The torque spec for the screws is 30 ft-lb for the M8 screws and 60 ft-lb for the M10 screws.