The standard issue of the GCE Vectrex software system artwork file, vectrex.zip limits all games to a common, generic bezel. That's how MAME does software system external artwork by default.
This is essentially a version of vectrex.zip that will allow each game associated with the Bezel Project GCE Vectrex pack to display it's own bezel at launch. Games that don't have a Bezel Project bezel will use the generic one.
Note that this is for use with MAME itself and is not compatible with RetroArch.
Once downloaded, the file MAME GCE Vectrex.zip should be unzipped.
The artwork file in the download is vectrex.zip and it contains the multi-view lay file.
The game bezels themselves are not included, due to permission from the Bezel Project to distribute them not sought, so you will need to download the pack and drop the bezels into the artwork vectrex.zip yourself.
You will also need to set LaunchBox Custom Command-line Parameters to allow MAME to match the correct bezel for each game. This is explained in the download.
The vectrex.zip artwork file will work whether you are emulating using direct media calls (games with the long naming and vec, bin, gam extensions) or emulating using a software list.
The lay is a single elememt one, as the Bezel Project pngs combine the actual bezel and the vectrex game overlay into one image.
Some other vectrex lays use two elements, where separate overlay and bezel images are used.
When checking out the Vectrex on-line, I got the impression that the game aspect was not 3:4 but slightly wider. I couldn't come up with an agreed answer so I went with 3:4.
So the game area is 810 x 1080 with an offset of 555 to centre it. If you want a wider aspect, then you need to increase the lay screen width (for all views) and reduce the X offset by half the width increase.