Fuel tank coating inside and out??

Ok this isnt mopar related, but any advice would help us mopar guys out as well! In Dad's 58 apache, he is thinking of having the inside of the fuel tank cleaned and sprayed/coated. Anyone see issues or can anyone recommend a product?? His fuel filter is coated in black junk, I think it might be from old fuel lines, but not sure yet. Thanks for the advice

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