You just need to bump the boot.img in the ROMI always use notepad++. I deodexed zv6 and finally got it to install but I get hit with an LG security error screen that bootloops. I checked my scripts, they're perfect. Tried the binary from the zv5 still the security error, and tried binary from zv6, same issue. I think something may have been patched to prevent a custom Rom from being installed. I know twrp is a bumped image, so I'm wondering if we need an oem unlock... I sure hope not. No boot.img we have will work either. I'm still digging into it, but I'm coming up empty handed right now.
Side note; I am stuck using Windows 7 to do all of this, so I'm keeping my fingers crossed and hoping that might be the issue.

edit: if you post a link to the zv6 boot.img, I can do it for you
I'm confident what ever they did can be reversed, and that the info to do it is in the zv6 update somewhere. We maybe able to create something that looks like an ota update to make changes to the bootloader is what I'm thinking. I'm just not sure how to go about it yet.