The short story is to use loboris’ image, and his uImage and script.bin files, and follow the instructions here.
Step 6 took place within the BOOT folder — so really just copying the uImage_OPI-2 file over uImage, and script.bin.OPI-PC_720p60 over script.bin. First make sure you’ve copied the most up-to-date versions of those two files into the BOOT folder.
My initial error on step 6 was to assume that I was copying from the non-SD location and copying onto the SD. So I started in dev/sda and tried copying into dev/sdb (i.e. BOOT)
I ran through all the steps using Lubuntu. It was quick and works.