Dan Graham wrote:

   Is this scheme even half-way sane?

Yes. It sounds correct.

   Is 16 blocks a large enough area?

Maybe. The superblock will be between 64KB and 128KB from the end of the 
partition. This depends on the size of the partition:

SB_LOC = PART_SIZE - 64K - (PART_SIZE & (64K-1))

So, by 16 blocks, I assume you mean 16 filesystem blocks (which are 
generally 4KB for ext3). So as long as your partition ends exactly on a 
64KB boundary, you should be OK.

Personally, I would err on the safe side and just shorten the filesystem 
by 128KB. It's not like you're going to miss the extra 64KB.

--
Paul