A good o-ring is all that is needed as long as the valve guides are not heavily worn.
The valve stems need some lubrication for a long life.
Personally, I am not a fan of modern positive valve stem seals on a 235. They seal too good for the amount of oil that is supplied to the rocker arm assembly in my opinion.
If you were to have the o-rings AND positive valve stem seals on a 235, you will not be happy with the results after a few thousand miles.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission