Just an update now about a year after my fuel valve rebuild. Only residual issue is that I cut the gasket for the valve from nitrile hoping to update the situation. (recall no one makes the gaskets for these valves anymore and one will have to be made from tracing the old one and raw materials).
I over tightened the nitrile making it squish out the sides some. This lead to the exposed part of the nitrile cracking. I am concerned that the cracking may migrate to the interior and lead to some leaking. So I am going to cut/replace the gaskets with new self made gaskets of gas proof carburetor material from the local auto store (a rubberized paper material; I think the original were cork).
I ran into this when installing CiEs probes I'm doing now. Their supplied nitrile gaskets at the tank adapter plate squished too much with the torque recommendations for screws. So mechanic and I eyeballed that and went lighter on the torque. Could still try to use nitrile but not be as aggressive with the screw down. But since valve near low point of system, going to go with the other material and make the screws "tight-tight".
also courtesy another member mention (Mr. Skymaster 337B) the following:
https://support.cessna.com/custsupt/...df?as_id=52067 (ME 81-19)
Not an expert but I don't think the models with simplified tank setup like G model have the unused port...