Nick,
I appreciate all the help you've given me. To be honest, I'm not sure if it is worth the effort. If you feel tired of this problem, I won't feel offended. I've spent a stupid amount of time trying to get a $10 device working. I don't want you to add to that time.
(I found that same Russian thread!)
I've got the rootfs you gave me earlier on a 2GB card and I've been able to copy your mtdblock6.img (ungzipped) to a directory on it. I can bootsd with it.
I've seen various references using dd if=N416mtdblock6.img of=/dev/mtdb... to write to the flash. However, I can't get past the part where the flash doesn't initialize properly and /dev/mtd4 and /dev/mtdblock6 are not available to that session.
Here's one reference that discusses mtd, but with tools I'm not familiar with:
https://bootlin.com/blog/managing-fl...ge-with-linux/