Yes you will need cable extensions. Measure the bars from tip (grip end) to about where the connector is on your bike. That will be your ballpark measurement.
Just did the Road 6, z-bars on my iron. I used the Burley extended kit. I did all internal wiring and it can be a bit of a pain with the z bars. Used a string to pull wires in and lots of we-40. It's much easier to put extended wires on after pulling the existing ones through the bars first. I watched a good video on YouTube on how to do it. If you have questions you can PM me and I'll try to help if you need. Good luck.....