Sometimes it's fun to answer a question that does not have a answer, or have an answer but no question. let me explain, in life we do things that are wrong and do things that are not; when it comes to cars, sometimes it does not matter.
Somebody asked the question of how to make the opening for a center filled tank that Porsche Race Department was commissioned to do when they created the light weight version of the 911. That meant a lot of items being deleted and made upgrades being integrated, we will focus on the center fill gas tank used on so many 911 now, only because it looks cool.
We have done this many times using a drill bit and a air reciprocate saw, it works for us and for other shops I've talked to, but there is a catch, a few reasons why this work for us and it may not work for you. First, we don't use the big hole saw you see on one of this pictures, that thing create a lot of heat and as you punch thru, it can damages the structure of the hood, leaving that are very flimsy. second, you think you have to cut a perfect circle, not really, just cut enough to give the filler neck clearance, cut small and make your way around it.
Make sure your tank is sitting properly and use a new seal, find a fiberglass or metal venturi looking section and weld or bond it to the opening and make sure it looks centered on the hood; There you have it, we have gone north, east, west and south and arrived in downtown at the same time. By the way, this made the short wheel base 911 R legendary !