Modes 74 and 748 are described here: https://uzebox.org/wiki/SPI_RAM_video_modes.
Mode 45 is somehow not documented in the wiki but it was used by his picture viewer demo: https://uzebox.org/wiki/Image_Viewer. Though boasting an impressive 232x200 4bpp, I appears to strictly be meant to be used to display preformated pictures.
I understand you built a Uzenet module already. Try the Akuma demo to see if it works. It's pretty simple and barebone. Eh, in that post I said SPI mode would not fly but mighty Jubatian proved me wrong. Btw if your module still doesn't work, your module soldering may need some checking (or the lines betwwen your header pins and the644).Actually, I do get a "NO SPI RAM!" error when I try to load UzeboxUI on my Uzebox