Suitable Vapor / Over fill valve for retrofit

That GM № 353162 ought to do exactly what you want. A detailed description of its function is At the gas tank a fuel separator valve is bolted onto a bracket near the top of the tank. A 3/8-inch hose on the bottom of this valve connects to a vent tube on the top of the tank and a 1/4-inch hose at the top of the valve connects to the steel tubing [that runs forward to the charcoal can]. The fuel separator valve has a float inside that closes the valve when liquid fuel floods the valve. This can happen from fuel sloshing in the tank or if the car is parked at an extreme angle. The valve prevents liquid fuel from entering the tubing and overwhelming the storage ability of the charcoal can. Obviously, being a float-chamber device, this valve has to be mounted topside-up.

It does not look as if the DV100 item will do what you want, and it would be a much bigger pain in the nuts to mount.

If you want to finish the job of closing the fuel system all the way completely, you'd want to adapt a '71-up pressure-vacuum fuel cap, and eliminate the vent tube that runs from the top of the filler neck to atmosphere. That's relatively easy on something like a '68 Dart (swap in a '72-'76 fillpipe and you're done). But it would be a major undertaking on something like a '68 Satellite (no same-body '72-up vehicle to get a dimensionally-correct fillpipe from) so instead, just reroute the end of that fillpipe vent tube. Presently it runs up about as high as the trunk allows so liquid gasoline all but can't get out, then makes a U-turn and goes back down, through the trunk floor, and just ends vertically under the car. All you have to do is connect that open end via fuelproof hose to a T in your vapour line running from your (new) separator valve forward to your charcoal can.

For those who don't know what in the Screaming Yellow Zonkers we're talking about: stopping an old car making its vicinity stink of gasoline. The retrofit info Mrmolding is talking about is here.