Jim,
I have some of the old "Redbird" style dry breaks and flapper valves that are useless to me since Nascar mandated the whole new fuel fill system with the ball check valve. You have asked about a fuel cell but be aware that these will only fit a true fuel cell, ballistic bladder and all, you are welcome to them if they will help. If that is all a little overkill, a one way flapper valve similar to this is available through Summitt or direct from Jaz Products. Depending on your application, that still may be overkill. I have always just used the old style vented gas cap for street use, never had any problems with inspection as older model replicas are not required to have a sealed cap.
