mounting quarter scoops

It sounds like you have a set of California Special scoops since I think even the '68 Shelby scoops were open, even though they were non-functional. The two screw dimples in front are the giveaway, since '67 scoops were mounted with two studs through the body. I used '67 scoops on my '68 and simply added a few strips of resin and 'glass mat to fill in the gaps, then sanded them to fit nicely. I'm not sure about the Californial Specials, but '68 Shelbys used a rubber gasket in between the scoops and the body, I'd bet it was more to hide the gaps than to actually seal the scoop to the car.