Lycoming recommends 425F or less in climb and 400F or less in cruise. You're not seeing any temperatures that are particularly concerning, although personally I do try to keep my head temps below 380F regardless of Continental or Lycoming. That said, when the 310 wasn't able to keep one of the heads on the left engine below 400F operating LOP on our trip up north earlier this week (remember it was rather hot), I didn't sweat it.
You will typically see a good variance between CHTs, simply because the cooling across the cylinders is uneven. As I said when I saw your plane earlier this week, it looks like your cowl inlets aren't as big as they were on the O-320/O-360 factory airplanes, and it wouldn't surprise me if, because of that, it doesn't cool as well. Having never flown in a 172 of any sort with an engine monitor, I can't comment.
I have found that on carbureted engines, especially these days, Precision has had poor quality control and different carburetors of the same model number on the exact same engine will produce different results as far as LOP/ROP. Next time I'm down by you we can go flying and play around with it.
Your engine won't explode, at least not because of what you're seeing.
