Hi there.
They are about 4 each from Ford new.
But this is one of the reason why the rocker cover gaskets fail they they are not getting the right tension from the fixing with the old bushing. They only get torque upto 10flbs or about 14nm but please check as its been a while since I have done this.
If you compare an old bush with the new bush the old bush is smaller, lost all its absorbing qualities by being almost solid and brittle.
Hope this helps