I must admit, that when developing the two libraries, I assumed that BaseType_t is at least 16-bits.
But please have a try and see how far you get.
What platform are you aiming at?
I have some FAT code that seem to work, and I am trying to get some FTP server to work right now. I could get back to you with more detailed information on what I have changed (so far).
It has 16-bit and 32-bit instructions, but it would be better to use 8-bit instructions since they may be executed in parallel and also make use of fewer registers. I.e. it is “the most efficient, natural type for the architecture” as the FreeRTOS documentation describes BaseType_t