You can use a FMC interconnect board to connect Xilinx KC705 with FX3. Please refer to the AN 65974 Section 10. ( Link is given below)
Thanks & Regards
I knew already about AN65974 cause I was previously using Xilinx SP601.
But now that I want to move over Kintex I was wondering if there was already an example (or apllication note) of KC705 and FX3 Explorer kit.