starting the FS1 construction

I'm only starting to get to the heart of the matter with this FS1L guitar that I've had since January ……. In the meantime I've found a neck with a Gibson-like head that I find better matches the shape of the body of this guitar.
I am at the adjustment of the handle in its housing I still have to sand a little so that the heel goes forward by 25 mm to be placed ‘’ perfectly ’’
During this phase I checked the alignment of the neck with the tailpiece and there must be a problem: by putting a ruler alternately on each side of the neck, the marking towards the tailpiece gives a difference of 4 mm which seems to show that the seat of the neck is offset by approximately 2 mm… apart from re-drilling the tailpiece attachment, is there a more elegant solution?
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Before starting the finish which I am thinking of doing with oil, I plan to put a veneer all around the body to hide the differences in appearance due to the assembly of different pieces of wood of the body structure, the first step is to remove a little material between the 2 bindings: the width is 35 mm with a depth of 0.4 to 0.5 mm (the veneer is 0.6 mm thick) again all advices are welcome!

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When I did my build I had the same issue where the opening was too narrow. You need slightly more width on the bass side for the wider string - otherwise your fretting finger will push it off the neck edge, if it's offset too much on the treble side file and block sand the bass side of the pocket. Don't sand the pocket floor though.

With this amount of offset this guitar plays good with great action. You see how there's just a touch more width around the low E
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thanks for your comment I'll try to go that way !