RE: Setting valves
The head is aluminum, the pushrods, etc are steel and cooled in the propwash. The aluminum head expands while the pushrods do not.
As engine temp goes up, the gap increases, not much but some.
Remember we use silicone exhaust diverters on glow engines and they are good to around 500 degrees, and that's well under any temp that a valve would burn at or even glow hot.
As long as you have some actual gap, it will be fine.