I haven't upgraded from 2007 and I'm not looking at the software just now, so I'll give you only general guidelines. You'll want to be sure you have 2 bodies (multi-bodies) and use the combine tool and the difference option. Try that.
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"Well, I've wrestled with reality for 35 years, Doctor, and I'm happy to state I finally won out over it." Elwood P. Dowd