How too Narrow a gas tank!

I plan on narrowing a brand new replacement gas tank for my 64 dart vert to allow for more tire room!
:???: The question is really how to go about it so I can keep the stock filler neck!

The plan is also to use an in-tank electric fuel pump, and new aluminum fuel lines!
Thanks

I would like to see this done. When relocating springs there's not enough room for the tailpipe on the passenger side. Please post some pics if and when you do it.