Difficulties with filling the tank all the way up

You didn't say what car or model year we're talking about here; but with that said, the early As ('66 and earlier) are much more prone to this due to their smaller fill tube diameter than later As with larger tubes, although they all still can act up with the higher nozzle pressures some stations use; as previously stated.
Layson's offered a modified fill tube (actually, I think it was a "send it in and we'll modify it) package that added an internal vent that addressed this problem. Not sure if they're still doing it, you could contact them or maybe @Rick@Laysons will chime in on this.
The Aussies have dealt with this for years, and even offered a drip shield to help avoid the dreaded "paint drool" on your quarters under the fuel fill.
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Kinda surprised nobody in the U.S. has picked up on these and offered repros. I'd really like to get one for my '66 wagon, which has REALLY goofy bends to it's fill tube and is especially prone to this...