Hy Village _Idiot, you may be able to find the original retaining clip, but if you can't you will need to put the lifter back together with a keeper, you may be able to go to an automotive machine shop in your area and ask if they have any hydraulic lifters that they are throwing away because they're worn out, you may find a suitable keeper that way. I'm not sure of your engine knowledge, but I will tell you an adjustment method that I have described to novices in the past. Wherever the engine has stopped, remove the distributor cap, and check to see if the rotor is pointing at a given terminal, If it is the trace the wire that is attached to that terminal, once you have identified the cylinder that that wire goes to you can adjust those two valves. On a hydraulic lifter engine I roll the push rod between my thumb and finger while turning down on the adjustment screw [after loosening the locknut a couple of turns] when the pushrod no longer wants to turn easily then you are at zero lash, after that point you can turn the adjusting screw one more turn and the tighten the locknut. You can turn the crankshaft until the distributor rotor lines up with each terminal in turn and adjust that cylinders valves in the same way until you have all six cylinders adjusted. I hope that helps.
