Not quite sure what you mean by that.. Now when someone ports your heads or intake they will port match it to a certian size gasket, Usually a Felpro 1250.
This is done to make sure you dont have a "shelf" in air flow. Maximize every last CC you can.
Don't waste your time. If you are going to port the whole manifold, then opening it up accordingly would only make sense. Opening just the mouth would probably hurt more than help.
Don't bother unless your going to remove the lower too. The real restriction is in the lower. If you match the upper, you'll blow aluminum up into the upper and unless you can hot-tank or parts wash the upper REALLY good, you could create problems. You can't match the lower to the upper cause you'd be letting shards go down the lower with no reliable way to get them out.