Would the gap be for the gasket?
There were never any gaskets used to mount these headlight bezels from the factory. They were installed directly to the fender sheet metal using standoffs. As far as finding these, look on eBay I see them pop up in NOS condition on occasion, however don't expect the quality of chrome to be as nice as having them re-plated, and the cost will most likely be what your paying to get these re-chromed.
One other thing that you need to verify should you stick with your plater is if he is truly a reputable shop when they plate these. There is an aesthetic trim edge that was casted into these bezels which runs along the top side of the bezel. When many platers redo these, they plate them with the typical copper, nickel and chrome and this decorative edge gets all washed out and blended into the rest of the surface and its filled in by the copper, nickel, and plating process of the bezel-this IS NOT how GM intended to have these produced. If your not concerned on true styling of how these were produced then this is of a big concern. However most platers are lazy and don't bother to make sure this styling trim edge is maintained in the bezel and will be careless to ensure its kept in the styling design as GM intended. You would be surprised how many cars I have see at shows that this has been lost. In concourse judging if the judge is truly paying attention they will note this error and deduct points. I'll bet there are other owners on here that if they check their bezels which were plated will see this styling edge has been lost. This also applies to Lemans and Tempest as they all shared this same bezel for 1966 and 1967.
I posted in this posting a pic (hard to see from an image I pulled from the Internet) which I hope you can see depicts this styling edge which washes out down the sides of the bezel.
I'm a very anal person when it comes to details and I think its in my Mechanical Engineering DNA for bringing this detail up, so am going to apologize if I come across on this site for noting this detail and sounding off like I'm the master-know-it all to all this info-just thought I would provide some heads up on this for those wanting to get this right in their restorations correctly and informing their plater when they get these re-chromed.