two quick pointers for you –
The .elf file of the official 1.02 OS can be downloaded from the same place as the .syx. However, it is not linked on the page (to avoid confusion) – use the same URL as for the .syx and change the extension to .elf. That way you are always on the safe side.
The HEAD of the CVS probably contains some work in progress, so its probably not the best choice.
Finally, in the file defs_general.h you can set the number representing the version, so you can label your own and keep them apart.