Yes, I thought amiga.lib might have something to do with it, that is why I was wondering how to check what is being linked in...now I know: you just use the 'Add library' menu item to add them. It was crashing before whenever I tried this. But I reinstalled StormC and it seemed to work, this has also fixed the other problem about the pragmas, I think I was using the NDK includes rather than those that are provided with StormC.
I'm not using any printf()-style functions for the 64-bit output, I've written a custom function which inserts thousands separators, etc. as necessary. And the user is already able to choose to view sizes in bytes, kilobytes, megabytes, or blocks.
Thanks to all those who have helped out...