I have always found it interesting how we can read things so differently. In my mind the word "match" is the limiting word here. It clearly defines how far you are allowed to go.
I think we would all agree that there is a definable difference between the word "match", the word used in this rule, and the word "enlarge", the word that could have been used if that was the intent.
Nowhere in the rule does it mention the word "gasket" at all. Maybe that is because gaskets are free so they really don't effect the interpretation of this rule.

Then just to be onery for the fun of it, the rule says that you can "match" to the "manifold". All cars come with an intake "manifold" and an exhaust "manifold". That is the exact wording used in my factory parts book to define the stock parts. We can clearly "match" to them.
Now, another rule allows us to use any any exhaust "header". The matching rule does not say we can match to the "header", just the "manifold".
It has long (even back with the rule was written) been a common defination when talking about car parts to refer to the stock exhaust cast part as an "exhaust manifold" and the aftermarket thin steel tubing exhaust part as a "header". Thinking of these common definitions, what does the rule, as written, actually allow?

I find it amusing how the IIDSYCYC applies sometimes in folks minds, and not at other times, depending on what they want to do, or have already done.
Carl