Yes - the 760/770/780 all support 3 way SLI.
Now I wouldn't suggest it... it's about a 5-10% increase over 2way and you're more than likely going to run into driver issues/freezes/etc etc etc.
If you already have 2 760 - sell the and purchase a 770 (even SLI) or 780.
Stay away from 3 way unless you're already at the "top" with 2 Way 780/Titan and have $ to burn.