Yeh that one is a toughie! When I was collecting Kenner it took me years to find an example!! Every MOC Bossk I found was either a 32 back or a Palitoy 45b!! I nearly settled for a Canadian 31 back. I managed to track down an AFA 70 example in the end. It was v nice unpunched, bubble and figure 85s but someone had put a hole punch through the unpunched bit and just caught a tiny bit of the main card 'Doh'!!
Since I changed my focus to Palitoy I have seen one or two more examples so stick with it. But out of the first 10 Empires on 31 I'd say Bossk was the toughest!!