If you're going to re adjust the lifters anyway I would go ahead and pull the pushrods out and check them to make sure none are bent. You're there already and it doesn't cost anything but a couple of extra minutes. I recently had a roller rocker fail and it was really bad. Worst noise I ever heard. You might inspect the distributor real well too. Pull it out and check the gear. If nothing looks amiss next step is to pull the intake and do a visual of the lifters and what you can see of the cam. You might want to take a look at the oil to see if there's any metal particles.