They most likely built the main car at the regular factory and then sent it out to a specialty shop to do the rest of the conversion....
When I worked at the truck plant, we did the Indy edition Ram 'sport' (the blue ones with the white stripes)... We built the main truck on the assembly line, but didn't install the unique front and rear bumpers and stripes... The unfinished trucks were then sent to a shop not far away called Cardinal Automotive to have the special bumpers and stripes and pace truck door decals installed... Cardinal was about 5 miles from the assembly plant...