If you can email the photos to me I will post them if you have problems.

I will try to get some pictures posted, however I am a bit challenged in that area.

The cap is vented. Evedently the innerseal [round piece of rubber] stops the sloshing enough so the cap seal can work as it should have initially.This is more of an inner baffle than a seal. The car has run for the best part of an hour with no tank preasure problems.

This sounds like a very cool and easy project. Does the cap still vent or is this for a non-vented system?

I am with Willie_B on this one. Could you post some pictures of what was done?

Don't forget the threadlocker.

Don't forget to check it periodically for deterioration. 

I am a visual guy. Any chance of some photos?

Sounds like a great project.

This morning I filled both tanks on my 67S to the very top. I then installed the gas caps with the "Smith seal" and took off down a piece of road I call the 5-mile test loop. This is  challenging and very curvy; in the past it always extracted a few pints of fuel. Upon returning to my shop I found no evidence of full spillage -- how sweet. For anyone interested, it is simple to make and install. For each cap, one#8 stainless machine screw, 1" x 32. 2 nuts for the machine screw, 2 ea 1.5" body washers. One piece of intertube rubber cut to the outside diameter of the gas cap. Drill and tap a hole to accept the machine screw on the inside of the gas cap center. Sandwich the rubber between the body washers and use one of the nuts to secure these pieces to the under side of the screw head. Now thread the other nut on the machine screw leaving about 1/4" of threads to screw in to the gas cap. When installed use this nut to lock down the machine screw to the gas cap. A drop of threadlocker on each nut and you are done. The rubber extends down into the filler neck about 3/4" of an inch, making a seal against the inner lip of the fuel filler neck. One 360 rotation of the gas cap to get the rubber in and attach the cap as usual. Thirty minutes from start to finish for both tanks and about $2 worth of parts.