Need help with FW upgrade of Dual X Carriage, Dual Z (no replies)

I built a Dual X Carriage with Dual Z Motors a few years ago and want to upgrade to the newest stable version of Marlin.

This is what I am currently running, 1.1.0 RC3 (i think).

Hardware is Oversized i3 with the following:
Azteeg X3 Pro with Viki 2
Dual X Carriage
Dual Z Steppers with Separate Endstops for leveling

Here are the questions that I have:

1. What version should I upgrade to?
2. Where do I find/put the pin assignments for the Extra Z and Extra X Steppers as the newer firmware just mentions that it will be assigned to the next E stepper.

I am not a programmer and it took me a few months to get it working the first time so I wanted to ask for help this time around.

Here is a link to my current firmware that is working (except for the basic buggyness). https://drive.google.com/open?id=1pPKD4ijfQ9fkFAYNaPhvg9hWHwB2qdae

Thanks for any help you can give.