There is no ability for a user to flash Verizon routers. All firmware updates are pushed from the Verizon infrastructure. Even if you could build an image, you can't load it.
Further, you can't build an image. The publicly available code is the open source code in the router. There most likely is proprietary code in the image as well, such as for the various network hardware blocks. Any proprietary code isn't in the tarball. I suspect there are security certificates in the image used for TR-069 and similar. The SoC may also use a secure boot process, which means the image needs to be digitally signed. If you don't have the public key for the digital signature, you can't make a bootable image. I doubt Verizon makes the public key, well, public.
I could be wrong about this, but from what I've seen the publicly available code is missing a lot of pieces. If you're able to figure out how to build an image and flash it without going through Verizon's servers you'll be the darling of the router hacking world.
Good Luck.
