TL;DR: I’ve managed to get the mainboard working the printed case.
First off, the red/blue flashing LEDs are (IMO) overly alarming for what they appear to be indicating. From what I have gathered from posts here, and the eventual change in behavior of the unit, is this LED pattern simply indicates that power has been connected while the main cover is off (or that there is no battery).
So, as odd as it sounds, ignore the flashing LEDs and connect your display and press the power button.
Once you can get the unit booting and displaying output (see items #2 and #3 below) you will likely be met with a screen indicating that there is no battery and that standalone mode is disabled. You can enable it at this point. Doing so will disable the red/blue flashing LEDs.
Second, as recently indicated, not all USB-C display options will display early (or as I like to classify them, core) screens. These include the initial logo display, BIOS/system settings, and pretty much anything else prior to the OS level drivers taking over. Note: eGPU output does not appear to be among those that can (or will) output the initial/core displays.
Third, the time to an initial display (if you have a compatible display device) is quite long 10+ seconds. You’ll have to be very patient.
Fourth, one can not boot most Linux installations without first disabling Secure Boot. Secure Boot can not be disable if any device has attempted booting. One either needs to start the system with no boot devices or mash F2.
Can’t seem to edit the original post title to indicate that this has been resolved.