Shouldn’t a second (flame) barrel and slightly modified brush guards for the headlights do the trick? I doubt anyone is going to looking for the filler cap for the flame tank. Even the brush guards could be modified with a file. As far as I am aware there are no other obvious external differences. The raised cupola of the M48 A3 Model B was also applied and just as relevant to the M67.
Extra barrel and brush guards, potentially two tanks for the price of one. Of course, if Empress choose to market it as a second kit, it makes no difference, folk will still buy a second item for the specific variant.