Personally I take each wire, and pull back an aluminum strand at a time. I cut each about 2-3 inches down so that the others will fit properly in the receptacle lugs. Electrical tape is your best friend and should not be used sparingly, although make it look good lads. I do not know what your 3wire, everyone has different names for wire.
Lugs and their counterpart the fitting are actually UL listed for specific gauge wire. You break code if you disregard factory listings. You can always pick up different size lugs terminations at the market for your job. Just remove the one screw holding the old lug and use that screw or a new one on the purchased lug termination.
They also make aluminum splices for going from aluminum to copper, they you wrap it it flex electrical tape. I see plenty of people make aluminum terminations to things rated only CU, or Copper terminations for things only rated AL.