Using a piston stop on smog heads

I am about to use a pro form piston stop on a goodwrech 350 with the 76cc chamber heads on it. I am doing this procedure with the engine in the car and the rockers all set since I have already had the engine running. With this style of head is there any way the piston stop will come in contact with a valve instead of the piston and cause damage as I turn it over by hand? Thanks.