Need info/advice re pulled rocker stud and probably stuck valves

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1968 with very fresh 327 - but sat quite a bit with only occasional start/warm ups and no road travel due to extended illness. Recently started up fine to load onto trailer for transport - a day later coming off the trailer I noticed miss due to valve issue. Could hear "clacking" - pulled the cover - intake and exhaust on single cylinder not moving because rocker arm studs pulled from head. Now - getting ready to repair.

1. Am I correct to think that the valves stuck and led to the stud pull-out - or??

2. If not stuck valves, what causes the stud issue?

3. My homegrown plan is to run Kroil down all valve guides (to head off sticking elsewhere) and let soak, remove the 2 offending studs and try using a dead blow hammer to see if those two valves will go down easily after the Kroil soak. Is this wise?

4. Want to replace those 2 studs with screw-in type - found the tools/studs online. Have you done this with head still on the block? Probably can trap shavings while tapping, but what are chances of shavings going through the tapped hole (is it open on bottom on original SB 327?)?

5. Is a valve seize event like this an indicator that some others are likely to follow - although I intend to try a run of top end lube after this fix.

5. Hate to do it on such a fresh rebuild, but is it best to take the head - or both heads - off and go though all of them - maybe put screw-in studs throughout? Is such an event anywhere near usual for an older SB design with pressed-in studs.

Thanks for wading through my questions. I need to do this right, but don't want to go into stuff not needed. All info/advice will be much appreciated. I need to get going on this one.