323 355 or 373 gears??

I am a little confused about the fuel tank question. Will the stock fuel tank work with a Dana 60? Was that the question ? Why would the differential make any difference ? Why would the stock fuel tank be a major concern ? Custom tanks are not real expensive in the total scheme of what you seem to be talking about with this build. Obviously the Dana was not an option so yours would need to be custom modified to fit, in which case you can make it any width that you want. Want it to launch and still cruise the hi-ways ? Get an overdrive from Gear Vendors. It will take any power you can throw at it, especially since you say it would be primarily a street car.
But you need a plan before you spend anything. To many different directions, need to narrow your wants to something possible and practical if you don't want to constantly change things.
(1) Result expected . (2) How much money are you willing to spend to get it.
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If you run a cast cover on a D60 with bearing supports and you car sits at a decent height it will the tank. YOu can often just roll the lip. OR just shim the rear back a touch.