Most of the latest amiga.lib is compatible with 1.3, but check the autodocs. You just need to make sure that the images created by the linker use compatible hunk types and offsets, that you have proper startup code, and that you don't try to use library functions that don't exist in 1.3.
EDIT: You might also want to avoid the C/C++ libraries included with most m68k-amigaos-gcc distributions unless you know the functions work on 1.3. Obviously, you want to stay away from ixemul, too, and you won't have bsdsocket. When in doubt, use Amiga-specific library functions.
