Stop in for a cup of coffee

It's the last 1/4 tank that matter the most to me to be accurate......and that is the "dead' zone. not a lot of difference.... Gauge has 2 adjustments on it, and you can do some adjusting on the sending unit itself... This is assuming full up is full in the tank and straight out is half. And full down is empty. Seems rigjt

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I don't how that works out on a '66. All (two, three?) measurements that were posted using a tank used a '67 up style.
The top portion is shaped fo the spare tire well.