Upgrade from ECX6.4.0 MR3P1 to ECZ7.3.0 P2 w/ Bootloader update - not able to load image - stuck at

I recently attempted to update an HA Pair of Net-Net 3820s that were running on ECX6.4.0 MR3P1 to ECZ7.3.0 P2 including having to update the bootloader(s) to accomplish this.  Unfortunately as careful as I was to follow documentation, I wound up not having them load the new image and they are currently stuck with console access only, and stuck at a prompt for Login, where none of the previously known credentials seem to be working.

I need assistance on how to proceed with fixing the image so they will boot properly again.  I make the assumption there is something I missed or which was not clear in the documentation when doing this, but I'm not sure how to get logged in to even check boot param, or bootloader.