I think you can use AmiDevc for ks 1.3, since Amiga (at least until 3.1) is backwards compatible. If you use functions and settings from Ks1.3 only, then your program should work from 1.3 up to and including 3.1. (I don't know the progress from 3.1 to 3.9 since I haven't received my Os3.9 from vesalia yet (after almost a month :-( ))
If you use other peoples source code, also make sure that they do not use any calls to newer functions.
The biggest changes seems to be in intuition and graphics library, whereas DOS and exec are pretty much the same for most applications.
best regards
