So I've been working on getting my GMC back road ready, was trying to diagnose a clack that to me sounded like a rocker arm slapping a valve. I'm a novice here so this was just my first guess and what I thought would be easiest to check. well I pulled the valve cover today and found that most of the valves had some lash in them and a couple were excessive. I went to tighten the rockers down and remove the lash when I found that one wouldn't tighten any more. Then I noticed it the stud is much higher than the rest so I started looking closer and I've got a few studs that aren't level with the rest. It seems that the rocker studs are backing out. What am I looking at to get these replaced? I read some older threads on here that said you can't really press them back in cause they'll just back right out again. Any estimate on how much it would cost to have a machine shop replace all the studs with screw ins? And if I do would this be the best time to replace/clean/refurbish/whatever the valves? I don't have a ton of money to dump into it right now. About 8 years ago I had a stuck thermostat and the engine temp got pretty high, but if I remember right it didn't get super high before I shut it down. Also any other general thoughts about the condition of everything seen in these pics I'm really trying to learn all I can and do things right. Also I'm seriously considering replacing all of the lifters since they're probably original.
Pics below. Thanks!