Farmall Cub

several of them were a fair amount under spec of 45 FT/LBS.

I don't really know how much in FT?LBS a fair amount is! Then again i have seen people reuse head bolts which is supposed to be a no no because of the stretch. Would we advocate removing, cleaning and adding sealant before reinstalling? Would we advocate replacing the ones a fair amount under spec? W ere they so loose one could fit a finger nail between the bolt head and the engine head?
As you can see from my earlier post on this subject I am skeptical that the retorquing will fully give the desired result but it just might help. Then again what type of sealant was used? Does it harden?

Too many questions for my little brain.

I used the aviation gasket sealer on the threads, but you could use PTFE pipe dope in a pinch.

If you have bolt showing a gap - yep you should dig deeper. Yes - I would not reuse head bolts, but only because of the corrosion - the ones I took off the '65 were necked down by corrosion. Head gaskets don't like the clamp removed off them, but one bolt may not cause an issue.