Uhum. KS 1.3 dos.library is anemic compared to KS 2.0+ one. So as a rule of thumb unless if the application uses stdio it won't work with KS 1.3.
Even exec library has tons of new stuff, such as AllocVec/FreeVec which are used extensively in newer programs. It is quite unlikely you could take some even remotely modern amiga application and build it easily for KS 1.3.
I have wondered about this previously. I was investigating the possibility of creating a link library for C that implements as much of the KS2.0 exec/dos library functionality as is reasonably feasible on top of 1.3. It would obviosuly have to provide replacement headers.
In the end, I didn't have any working 1.3 machines to test the idea.
