Stepside Filler and Tank (gas slops out the filler)

[76C10Stepside]

My '76 C10 stepside has one small gas tank on the right side of the frame, and filler hole is very low down on the fender. When I fill it, I have to kneel down, and I can't hold the filler spout upside down, because gas will shoot out if I do.
Also, if if fill the tank until the guage reads full (even though I'm pretty sure it's NOT full), gas slops out the filler hole when I turn left, until the level goes down aways. I NEVER fill it all the way up, only put $20 or sometimes $25 if it's really on "E".

This truck has dual exhaust and a heavy duty trailer hitch, so no room between the frame rails for a center-mounted gas tank.

Is there a cure for this problem, like moving the filler hole UP? Do the later stepsides have the filler hole higher on the fender?