If you pull the heads to replace the gaskets, you should check the deck with a straight edge. Look especially close at the four
oil passages going to the heads. The deck should be perfectly flat and not scratched up. See if you can slide a 0.001" feeler gauge under the straight edge in the area of those
oil passages, that head bolt hole, and the near by water jacket. If 0.001" will slide under increase the sizes until you find which one will not fit. That will tell you how far the deck is from flat.
If it is not flat is should be milled flat, but if you cannot afford it, I would consider a thin coat of a good RTD in the low spot. You want just enough to fill the low spot and not quirt else where.
Also look for a crack in the block with bright lights. If you find nothing wrong, you may want to pull those restrictor tubes and replace them with ones that are long enough to go almost to the cam. Then seal them in place, like was mention in the other thread that I put a link to above.