Hello first time posting here.

I have a question about mating. I have started a porject desiging a V8 motor. I am tring to mate the pushrod to the rocker arm, as well mating the intake valve stem to the rocker arm as well. I am having issues with what type of mate i would use as well keeping them moveable. 

I have attached some pictures of the rocher arm , pushrod, and valve stem. So far all the moving part rotate correctly IE: Crack, cam, pistons, lifters, pushrods.