I wanted to report back that today I got the 60-day carrier unlock texts from Tracfone, which worked fine for both the 8GB and 16GB T408DLs, then I went forward on rooting for the 16GB, with the 8GB for a future date. I used the python version of the autobooter on a Linux notebook, which put the phone in fastboot mode, then "fastbootd" mode for speed, permitting me to flash the neutron.img for Magisk in just a few seconds. (The flash did a "factory reset" of sorts, but the phone was still carrier unlocked.) It took a couple of boots, but I got Magisk fully installed, was able to "su" an "adb shell", write-enabled the system, then got developer mode working. That's proof-of-concept for me. I'll get more into it later.
Thanks again to everyone who made this possible.