Fuel Injection Tank question

[THI]

I have a 1978 GMC K25 from Arizonia that I am going to resto-mod if you will. I have a Dana 60 rebuilt and ready to put on it and currently am taking the body off the frame so it can be cleaned up and painted. When I put things back together I will eventually put either an LG4 I have laying around, or the 8100 Gen VII Big Block I am removing from a 2003 2500HD - leaning towards the 8100!

Here is the issue, I know I can run the 1987-1991 TBI tank selector valve and TBI tanks with 1996-1999 Vortec pumps and sending units. The problem is I cannot find a fuel filler hose that will go from my original fuel filler to a tank with the larger opening. If I had a 1979 or later I would replace the fuel filler neck to a 1982 and later, but my current fuel filler necks are in great shape as is my original box.

What are folks with the 1973-1978 boxes doing for fuel injection tanks? Thanks. Tom