"leak just a little"
That's a can of worms!

Sure, go ahead and lap but if after 20 or so seconds if you don't get good contact patterns on each side they need more attention.

Keep in mind that as valves heat and expand more than the heads, the lapped areas will probably not be in contact with each other any more.

The holes are for AIR injection. Mopar ran the air into a separate passage in the exhaust manifold, then into the head exhaust ports through those holes. I drilled them out, tapped for 1/4-20 threads, then screwed in some junk screws and cut off the heads. Done. Use thread locker? Hardly necessary. But when threading, use plenty of lubricant. I managed to break off a tap in one of the holes. That one I plugged from the inside with some goop I had around.

Seeing how easily they plug with carbon I am sure just filling them with JBWeld would suffice in blocking them off.

R.