F tank is identical to K7/8 tank EXCEPT the petcock.
Cb550F carbs, 069A are fed with two tubes from petcock.
K7/8 PD Carbs are fed with one hose therefore petcock on 75-77 F models are different than K7/8 petcock.
Anything can be fixed and customized, as long as you know what needs to be done.
I had used a k8 tank on my 75F by using a fuel line T to combine hoses from carbs and then one to petcock.
Cheers
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