In '71 I watched Earl use the oil method at least 2 or3 times, maybe more, on an entry following record runs. Kept coming up just a couple or so cc over so he suggested they pull the head for measurement which they did, mic'd out the same couple or so cc over. Earl was as disappointed to have to disallow the record because of being so close on the wrong side as they were to have missed the mark.
Granted there is no replacement for displacement but I think just as much, if not more, additional power from a .010 over bore comes from making the hole round again after an engine has been heat cycled a few times as from the displacement increase. If possible I'd stay away from the absolute upper class displacement limits just to make life easier all around. Just my 2 cent opinion.
Ed