However, several of the steps in that guide I didn't have to use at all, so I'm documenting my process here. To be fair, a lot of my instructions and the guide I initially followed, can be found here.
#Refind boot manager breaks linux mint install
WARNING: Do not proceed with any of these steps unless you have the ability to restore a bare-metal backup.
Needless to say, I failed miserably when I opted to have Kali install Grub and it overwrote my primary Boot Manager on the Mac and rendered the system unbootable (and eventually unrecoverable). So, I set about working on a dual-boot scenario.
I originally thought I'd just build it into a Virtual Machine (using Parallels), but was concerned that I might not have the control over the hardware that I'd need in order to make Kali effective as a learning environment. I recently decided to run Kali Linux on my MacBook.