Couple different ways to do it BUT the most important is to pull the plugs, take an old spark plug and weld an air chuck onto it and then fill the cylinder with air so that the valve won't drop down when you undo the keepers. One of the tools is just a flat plate with a slot in the middle and a hole on one end. You remove the rocker, place the hole of the tool over the rocker stud and replace the rocker nut. Now the slot will be over top of the spring which you can compress and pull off the retainer and replace the keepers on that spring. Or the other tool is just like a small gear puller which you screw down over the valve spring to compress it. If the keepers came loose and made the rocker arm twist, that would bend your pushrod. Maybe replace the rocker and pushrod as well.
