As long as it doesn`t hit hardware registers,etc and do calls to specific OS3.x libraries,it must work well under emulation.If you want to start new projects,and want to do as much portable as it can,you need to stay away from 68k ASM and trying to code something in C using latest OS3.9 environment libraries & functions aswell,then it can work well in OS4 and easily be ported to OS4 Specific new features.
