Maybe you should have your dad read this article at Jim Carter's Classic Truck Parts website:

http://www.oldchevytrucks.com/cgi/htmlos.exe/001701.2.4422491836200000104

If the link above does not work, follow directions to read the article:

http://www.oldchevytrucks.com

Technical Articles

1955-66

In-Cab Gas Tanks

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Good luck getting the '64. smile

-W