I plan on talking with the local FSDO

Then you will never be able to do it. Never. Once they know you had
plans to do it, you lose plausible deniability.

Look, here's the way it is. All alterations to the fuel system are
major. You have no approved data. You have an unapproved part. It
would take an STC or field approval to make it happen, and you won't
get one. You're stuck with either your obsolete, leaky, marginally
safe - but legal - valve, or you make the alteration yourself, by dark
of night, and don't tell anyone. And make sure you have the kind of IA
who doesn't notice such things.

Michael