So I went ahead and wrote up a spec that's a hybrid of two other filesystems. It's simple to implement on an 8-bit system, and allows for large files for later projects. Each I-Block can define a file 36MB in size, but I-Blocks can be chained together in a linked-list to allow files up to 8.5GB in size. It can even address a 2TB volume right out of the gate. All of this with pretty small overhead for each file, and very little overhead for the filesystem itself.