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My new Dansk tank will be installed in the next 2-3 weeks will let you know.
empty the tank , cut the nek off , use a tube a little bit larger and slide it over the cuted piece , adjust the nek in a perfect position , weld everything back togerther , i would do that , its much cheaper as a new tank ,
Some of those early reproduction fuel tanks had filler necks that were too short - you could have one of them.
For what it's worth I have a used tank that is full of holes, but you may be able to use the neck off it and fit it into yours. It isn't available just yet as I want to trial fit my new tank before I junk this one just in case, so it will be a few months before I can get rid, but if you are not in a rush the offer is there.
...funny how I'm fixing all of the previous "restoration" work! The tank now is just a bit north of $1,000. If Scott's filler neck doesn't work out, I may have to just buy the OEM tank.