Do lifters/HLC's/ball studs need to be prepared before installing?
 

I was wondering if they should be soaked in oil before putting them in, to kind of pre-fill them, or do I just pull out the little plastic plug and screw them in? I'm working on a tapping on the '86 560SL, 117 engine.
Do I need to replace the rocker too, or just the lifter if the rocker is in good shape?

Just put them in the way they come out of the box. No need to replace the cam follower if there is not a problem. Good idea to check to see if any changes in the shim are needed.