Well scratch that.
I put my flashing machine back together, and installed two 3C905CX-TX-M
cards, and they are now autodetecting their flash chips; I have no idea
why it didn't work the other day.
I think I'll try installing a socket tomorrow and see if it will work
with larger chips ( i'm unsure whether the >512kbit addr line(s) are
drawn out to the flash or not ).