No cutting needed.
The tank has a metal tube welded to it, a rubber hose fits over it, the fuel filler slips thru the hole in the cab and into the rubber hose.
The fuel filler tube you need isn't shown in the LMC catalog. But I am sure there are a couple thousand in salvage yards.
You might try emailing Tony Smith at
4-5-6chevytrucks@sbcglobal.net I am sure he can hook you up with one.
Tell him lakeroadster sent ya!