Peter,
What you suggest is what I've done today. The FAT seems to start at 300600x and again at 301240x offset. I can see the difference in sector counts (4C 24 EC 00 for the 8GB and 5D F2 94 00 for the original 5GB).

Occurred to me after editing the quantity of sectors (but not the sectors per FAT) that even if I did modify this, the origial FAT file descriptors would be in the wrong locations (I assume you'd need twice as big descriptor table to handle twice the addressed space).

However, I may wait till Monday, since I do see a few other differences early on (0x06 0x07 and 1F0x0B, 1F0x0C) but I can't figure what they mean; I'm looking for values with a ratio of approximately 0.625 (5/8) for the 5 and 8GB drives.

Mmmm pesto!

-Zeke