OK, after finding that the 64-bit Magisk GApps module likely will not work with the 32-bit armv7l T408DL, I looked for another path to GApps. Unfortunately I won't be able to test it for another month, until my phone becomes carrier unlocked, when I'll be willing to try things. Hopefully someone else can try it in the meantime and report back.
There is a Magisk module called Magic Flash [Login to see the link]. When installed in Magisk, a command shell (like "adb shell") should have access to a "flash" command line that will install zips, just like a custom recovery. There is a XDA post about it [Login to see the link].
Once the "flash" command is available, my hope is that it would be able to install GApps, like the OpenGApps for arm 11 available [Login to see the link].
Again, I'm not able to test it right now. Good luck to whoever does.
