Now that you've put up a pic we can see what your limitations are. By the "Lobeck" light I presume it's a knockoff of the "hollywood" style that mounts above the plate? How about twisting your thinking a bit. Back in the era you want to emulate there were also lights mounted to the side. You might have to fabricate a backer panel for behind the plate (aluminum, steel, whatever works for you) with a couple "wings" to mount the light units to.
Here are a few examples;
http://www.jcwhitney.com/chrome-lice...&redir=k232270

http://www.amazon.com/RoadPro-RP-107.../dp/B001JT3DNC

http://www.etrailer.com/p-LP71CB.html

And with some searching you can find many more styles.

Or, there's this motorcycle unit that could be very clean, mount two, one on either side; http://www.customdynamics.com/illumi...nce_plates.htm
the one nearly halfway down the page identified as "vertical".